DOCSLIB.ORG

Outlines of the Development of the Tuatara, Sphenodon (Hatteria) Punctatus

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Outlines of the Development of the Tuatara, Sphenodon (Hatteria) Punctatus Outlines of the Development of the Tuatara, Sphenodon (Hatteria) punctatus. By Arthur Demly, D.Sc, Professor of Biology in the Canterbury College, University of New Zealand. With Plates 1—10. TABLE OF CONTENTS. TAGE 1. PREEACE . .1 2. INTRODUCTORY REMARKS . .4 (a) On the Habits of the Tuatara . .4 (A) On the Time occupied in Development, with List of Embryos classified and arranged in Chronological Order . 9 (c) On the Structure of the Egg . .11 3. SYSTEMATIC ACCOUNT OF TIIE STAGES IN DEVELOPMENT . 14 4-. SUMMARY AND DISCUSSION OE PEINCIPAL EMURYOLOGICAL OBSERVA- TIONS . .60 («) The Formation of the Germinal Layers . .60 (6) The Formation of the Foetal Membranes . .05 (c) The Modelling of the Body, and the Foundation of the Princi- pal Systems . .69 (d) The Embryonic Colour Markings . ,77 5. LIST OE REFERENCES . .79 6. DESCRIPTION OP FIGURES . .SO 1. PREFACE. SHORTLY after my arrival in New Zealand my friend Pro- fessor G. B. Howes, LL.D., F.R.S., urged me to undertake the investigation of the development of the Tuatara (Sphe- nodon punctatus), but for various reasons I decided at that time not to do so. Some time afterwards, however,while examin- VOL. 42, FART 1. NEW SER. A 2 ARTHUR DENDY. ing the parietal eye in some embryo Australian skinks, I was struck -with the existence of an optic cup, apparently similar to that of the paired eyes. This seemed so startling that T resolved to attempt to obtain Tuatara embryos for the purpose primarily of studying the development of the parietal eye. Knowing that Stephens Island, in Cook Straits, on the recommendation of the Australasian Association for the Advancement of Science, bad been proclaimed a reserve for the Tuatara, it occurred to me by a happy inspiration to address a letter to the lighthouse keeper, then entirely unknown to me even by name, asking bis assistance in the matter. I wrote to him first on July 3rd, 1896, and most fortunately I found in Mr. P. Henaghan, the principal keeper on Stephens Island, an ardent enthusiast, who threw himself heart and soul into the work in the interests of science; and I cannot sufficiently express my gratitude to him for the magnificent supply of material which he obtained for me, and also for the valuable information which he gave me from time to time in his in- teresting letters regarding the habits of the Tuatara. Stephens Island being now a reserve, it was of course necessary to obtain permission from the New Zealand Govern- ment to collect, and this, through the kind assistance of Sir James Hector, F.R.S., was successfully accomplished. To the Hon. the Colonial Secretary and to Sir James Hector I also wish to express my gratitude for their courtesy. I had proposed visiting Stephens Island myself during the breeding season, which was supposed to begin about January, but pressure of other business made it very difficult for me to do so, and I ultimately resolved to trust entirely to Mr. Henaghan for the supply of eggs. There is regular com- munication between Stephens Island and the mainland only once in six weeks, so tlicit considerable difficulty and delay were experienced in sending the eggs, in consequence of which a considerable number perished. Several lots of the eggs were sent packed in moss or lichen in tin cans, but they were very liable to go bad in this packing if delayed OUTLINES OE THE DEVELOPMENT OF THK TUATAEA. 3 on the voyage, and subsequently we found that much the best way was to pack them, only a few together, in tin cans filled with the coarse brown sand which occurs on the island. Thus packed they travel admirably. I found it quite possible to keep the eggs developing, buried in damp sand after their arrival, but this was attended witli considerable risk, as they are very subject to the attacks of mould if kept too damp and without sufficient ventilation, while they readily shrivel up if allowed to get too dry. The first consignment of eggs was received about the end of January, 1897. Unfortunately the embryos all died, appa- rently from drying up of the eggs, before they reached Christ- tihurch. Nevertheless one advanced embryo, the only one as yet obtained of Stage Q, was removed from the egg in-suffi- ciently good condition to be of considerable value. I obtained no more eggs that summer, my arrangements being interfered with by a German collector, who visited Stephens Island about the new year, having obtained a recom- mendation to the keeper from the authorities. The only other eggs found that summer were forwarded to him, but I am informed that they perished in transit. The next eggs which I received arrived, greatly to my sur- prise, in July, 1897, a season of the year at which we did not at all expect them. They were only three in number, and con- tained very advanced embryos (Stage K.) in excellent condition. In November, 1897, the work began in earnest, and from that time to the present I have received consignments of eggs at more or less frequent intervals. Latterly I have requested Mr. Henaghan, when he finds a nest, to keep the eggs on the island, to continue their development, and send them on to me at intervals in small quantities, a plan which we find to work admirably, and which I regret did not occur to me before, as all the embryos thus obtained have been in much the same advanced stage in development, and some more of the earlier stages would have been more useful. The result of our operations, however, has been to secure a magnificent series of embryos, the majority of which hnvp heen 4 AETHUK DENDY. hardened in Kleinenberg's picric acid after removal from the egg, and preserved in alcohol. Those which were required for sections were stained with borax carmine, and cut in paraffin with Jung's sliding microtome. I found it desirable to use oil of cloves for clearing the embryos previous to embedding in paraffin, as this allowed of more advantageous examination of them as transparent objects than the turpentine method which I usually employ. It would, of course, be impossible in the time which I have had at my disposal to give anything like a complete account of the development of the Tuatara; and in this communication I propose only to give a general outline, with special reference to the formation of the germinal layers, the foetal membranes, the modelling of the body, the foundation of the principal r.ystems, and the classification of the embryos into stages; which will, I hope, be useful in future investigations either by others or by myself. This general account may be followed by more special memoirs dealing with the development of the particular organs. Already, indeed, I have sent home for publication one such memoir " On the Development of the Parietal Eye and adjacent organs." In concluding this preface I must express my sincere gratitude to Professor G. B. Howes for his kindly interest and encouragement, and for revising the proof sheets, and super- intending the execution of the plates in my absence from England. At my request he has undertaken to investigate the deve- lopment of the skeleton, and for this purpose I am forwarding to him a supply of material. 2. INTRODUCTORY REMARKS. (a) On the Habits of the Tuatara. Since I have not myself visited Stephens Island, it will be as well to give the following account of the habits of the Tuatara as nearly as possible in Mr. Henaghan's own words. OUTLINES OF THE DEVELOPMENT OP THE TTJATARA. 5 "Our island," writes Mr. Henaghan,1 "is densely covered with scrub of various kinds; the soil is good in most places, especially on the ridges; in the gullies the soil is of a light brown colour, largely composed of oxide of iron. The birds and lizards burrow into this soft soil, and one can often find both living peaceably in the same hole. There are three or four kinds of petrel frequenting the island, and if you were here now, which is their breeding season, you would be sur- prised at the numbers of them,—there is hardly a foot of soil but is undermined with their holes. Insects of various kinds are also well represented, and I think the lizards feed largely on them, especially beetles. I believe they also eat young birds,—in fact, I have seen them do it.s They, however, live a large part of the year without any food, keeping constantly to their holes. There are three or four kinds of lizards here alto- gether, the Tuatara being the largest; the others are very small. There have never been many lizards' eggs got here yet, though the Tuataras are very numerous." The breeding season apparently commences in November on Stephens Island, and each female lays about ten (10) eggs.3 On November 1st, 1897, Mr. Henaghan removed ten eggs from an individual which had probably been accidentally Crushed by a cow. These eggs, which were forwarded to me, were apparently quite ready to lay, but in the one which I Opened on their arrival I found no embryo, and the others unfortunately went bad subsequently, instead of continuing their development, as I hoped they might. The ground, Mr. Henaghan informs me, is so full of holes that one has to dig ever so many before finding a Tuatara, and then the probability is that it will turn out to be a male, these being far more numerous than the females.
Load more

Recommended publications
  • 3 Embryology and Development
    BIOL 6505 − INTRODUCTION TO FETAL MEDICINE 3. EMBRYOLOGY AND DEVELOPMENT Arlet G. Kurkchubasche, M.D. INTRODUCTION Embryology – the field of study that pertains to the developing organism/human Basic embryology –usually taught in the chronologic sequence of events. These events are the basis for understanding the congenital anomalies that we encounter in the fetus, and help explain the relationships to other organ system concerns. Below is a synopsis of some of the critical steps in embryogenesis from the anatomic rather than molecular basis. These concepts will be more intuitive and evident in conjunction with diagrams and animated sequences. This text is a synopsis of material provided in Langman’s Medical Embryology, 9th ed. First week – ovulation to fertilization to implantation Fertilization restores 1) the diploid number of chromosomes, 2) determines the chromosomal sex and 3) initiates cleavage. Cleavage of the fertilized ovum results in mitotic divisions generating blastomeres that form a 16-cell morula. The dense morula develops a central cavity and now forms the blastocyst, which restructures into 2 components. The inner cell mass forms the embryoblast and outer cell mass the trophoblast. Consequences for fetal management: Variances in cleavage, i.e. splitting of the zygote at various stages/locations - leads to monozygotic twinning with various relationships of the fetal membranes. Cleavage at later weeks will lead to conjoined twinning. Second week: the week of twos – marked by bilaminar germ disc formation. Commences with blastocyst partially embedded in endometrial stroma Trophoblast forms – 1) cytotrophoblast – mitotic cells that coalesce to form 2) syncytiotrophoblast – erodes into maternal tissues, forms lacunae which are critical to development of the uteroplacental circulation.
    [Show full text]
  • MA 5.4 NUMA SI GA RBHAVIKA S KRAM Completed Fetus in Prsava- Vastha Rasanufj*^SIK GARBHAVRUDHI
    MA 5.4 NUMA SI GA RBHAVIKA S KRAM Completed Fetus in prsava- vastha rASANUfJ*^SIK GARBHAVRUDHI I N Ayurvedic classics, the embryonit*««,^jie.uaJf6f'ment has been narrated monthwise while the modern Medical literature has considered the development of embryo in months as well as in weeks. "KALALAV/ASTHA (first month) ^ T ^.?1T. 3/14 Susruta and both Vagbhattas us.ed the word 'K a la la ' forthe shape of the embryo in the first month of intrauterine life. I Caraka has described the first month embryo as a mass ofcells like mucoid character in which all body parts though present are not conspicuous. T Incorporated within it all the five basic elements, ' Panchmah'abhuta' i.e. Pruthvi, Ap , Teja, Vayu and Akas . During the first month the organs of Embryo are both manifested and latent. It is from this stage of Embryo that various organs of the fetus develop, thus they are menifested. But these organs are not well menifested for differentiation and recongnisiation hence they are simultenously described as latent as well as manifested. 3T.f.^. 1/37 Astang - hrudayakar has described the embryo of first month as 'Kalala' but in 'avyakta' form. The organs of an embryo is in indistingushed form. Modern embryologist has described this first month development in week divisions. First Week - No fertile ova of the first week has been examined. Our knowledge of the first week of I embryo is of other mammals as amphibian. The egg is fertilised in the upper end of the uterine tube, and segments into about cells, before it I passes in to the uterus, it continues to segment and develop into a blastocyst (Budbuda) with a trophoblastic cells and inner cell mass.
    [Show full text]
  • Formation of Germ Layers (Second & Third Week of Development)
    8.12.2014 Formation of Germ Layers (Second & Third week of Development) Dr. Archana Rani Associate Professor Department of Anatomy KGMU UP, Lucknow Day 8 • Blastocyst is partially embedded in the endometrial stroma. • Trophoblast differentiates into 2 layers: (i) Cytotrophoblast (ii) Syncytiotrophoblast • Cytotrophoblast shows mitotic division. Day 8 • Cells of inner cell mass (embryoblast) also differentiate into 2 layers: (i) Hypoblast layer (ii) Epiblast layer • Formation of amniotic cavity and embryonic disc. Day 9 • The blastocyst is more deeply embedded in the endometrium. • The penetration defect in the surface epithelium is closed by a fibrin coagulum. Day 9 • Large no. of vacuoles appear in syncytiotrophoblast which fuse to form lacunae which contains embryotroph. Day 9 • Hypoblast forms the roof of the exocoelomic cavity (primary yolk sac). • Heuser’s (exocoelomic membrane) • Extraembryonic mesoderm Day 11 & 12 • Formation of lacunar networks • Extraembryonic coelom (chorionic cavity) • Extraembryonic somatic mesoderm • Extraembryonic splanchnic mesoderm • Chorion Day 13 • Implantation bleeding • Villous structure of trophoblast. • Formation of Primary villi • Secondary (definitive) yolk sac • Chorionic plate (extraembronic mesoderm with cytotrophoblast) Third week of Development • Gastrulation (formation of all 3 germ layers) • Formation of primitive streak • Formation of notochord • Differentiation of 3 germ layers from Bilaminar to Trilaminar germ disc Formation of Primitive Streak (PS) • First sign of gastrulation • On 15th day • Primitive node • Primitive pit • Formation of mesenchyme on 16th day • Formation of embryonic endoderm • Intraembryonic mesoderm • Ectoderm • Epiblast is the source of all 3 germ layers Fate of Primitive Streak • Continues to form mesodermal cells upto early part of 4th week • Normally, the PS degenerates & diminishes in size.
    [Show full text]
  • The Duplication Op Male and Female
    THE DUPLICATION OP MALE AND FEMALE EXTERNAL GENITALIA: With Records of Two Cases, by THOMAS GILCHRIST, M.A., M,B«, Ch.B. THESIS for the Degree of M;D; September, 1932. ProQuest Number: 13905404 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a com plete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. uest ProQuest 13905404 Published by ProQuest LLC(2019). Copyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States C ode Microform Edition © ProQuest LLC. ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106- 1346 CONTENTS. Page Introduction ... ... 1. A. Duplication of Male External Genitalia 6. Historical Notes ... ... • • • 7. Summary of Recorded Cases ... 24. Description of Author1s Case ... 29. Post-Mortem Examination ... 33. Family History ••• ••• 37. B. Duplication of Female External Genitalia 41. Historical Notes ... ... ... 42. Summary of Recorded Cases ... 53. Description of Author's Case ... 56. Po81-Mortem Examination ... 60. Family History ... ... 68. II. Page G. DISCUSSION «*« •. * ••• i»* ••• 70. EMBRYOLOGY .............. 71. Early Differentiation of the Embryonic Area .♦• 71. The Development of the Posterior Aspect of the Yolk Sac *• i»* ... 77. The Development of the Urogenital Organs •., 85. EXPLANATION of the ABNORMALITIES 89. SUMMARY * 11 * * * • * * .«. 117. BIBLIOGRAPHY 121. III. I ILLUSTRATIONS. Figure Page 1. Photograph of Author* s Male Case of Duplicated External Genitalia 30.
    [Show full text]
  • Overview of the Development of the Human Brain and Spinal Cord
    Chapter 1 Overview of the Development of the Human Brain and Spinal Cord Hans J.ten Donkelaar and Ton van der Vliet 1.1 Introduction tant contributions to the description of human em- bryos were also made by Nishimura et al. (1977) and The development of the human brain and spinal cord Jirásek (1983, 2001, 2004). Examples of human em- may be divided into several phases, each of which is bryos are shown in Figs. 1.1 and 1.2. In the embryon- characterized by particular developmental disorders ic period, postfertilization or postconceptional age (Volpe 1987; van der Knaap and Valk 1988; Aicardi is estimated by assigning an embryo to a develop- 1992; Table 1.3). After implantation, formation and mental stage using a table of norms,going back to the separation of the germ layers occur, followed by dor- first Normentafeln by Keibel and Elze (1908). The sal and ventral induction phases, and phases of neu- term gestational age is commonly used in clinical rogenesis, migration, organization and myelination. practice, beginning with the first day of the last men- With the transvaginal ultrasound technique a de- strual period. Usually, the number of menstrual or tailed description of the living embryo has become gestational weeks exceeds the number of postfertil- possible. Fetal development of the brain can now be ization weeks by 2. During week 1 (stages 2–4) the studied in detail from about the beginning of the sec- blastocyst is formed, during week 2 (stages 5 and 6) ond half of pregnancy (Garel 2004). In recent years, implantation occurs and the primitive streak is much progress has been made in elucidating the formed,followed by the formation of the notochordal mechanisms by which the CNS develops, and also in process and the beginning of neurulation (stages 7– our understanding of its major developmental disor- 10).
    [Show full text]
  • 2. Blastogenesis. Implantation. Gastrulation. Notochord. Somites
    Z. Tonar, M. Králíčková: Outlines of lectures on embryology for 2 nd year student of General medicine and Dentistry License Creative Commons - http://creativecommons.org/licenses/by-nc-nd/3.0/ 2. Blastogenesis. Implantation. Gastrulation. Notochord. Somites. Upon fertilization − restoration of the diploid number of chromosome − individual karyotype (set of chromosomes) completed − chromosomal determination of sex of the new individual (46 XX, 46XY) − mitoses = cleavage − zygote → blastomeres, un#l the day 4 s#ll within the zona pellucida o 30 hours: 2 blastomeres o 40 hours: 4 blastomeres o 3 days 16 blastomeres = morula − day 4 o late morula hatchin from the )P o cavities fusin into blastocoelom " blastocyst − day 6: outer + inner blastomeres et specialized to: o trophoblast cells later on ives rise to extraembryonic structures, fetal membranes o embryoblast later on ives rise to epiblast and hypoblast (embryonic,animal pole) Cleavage and gastrulation in man − oocyte o oli olecithal (little yolk only) o isolecithal (even distribution of yolk) − cleava e o total (the whole volume under oes the cleava e) o e-ual (uniform size of blastomeres) − astrulation o .euterostomia (Echinodermata, 0emochordata, 1hordata) o delamination (mi ration of cell layers) instead of inva ination Morula and blastocyst − day 3: 16 blastomeres = morula − day 4: o hatchin of the late morula o outer cell mass = trophoblast o inner cell mass = embryoblast o blastocoelom " blastocyst Implantation (nidation) − mostly in anterior or posterior uterine wall, in the cranial third of the uterine body − cave: ectopic implantation ( raviditas extrauterina 2 3E4) − day 6211 − adhesion of the trophoblast to the endometrium (secretory phase) o selectins produced by the trophoblast bind the oli osaccharides on the endometrial surface 1/5 Z.
    [Show full text]
  • BIOLOGY – DIVE INTO LIFE Mycareers.Pk
    2019 BIOLOGY – DIVE INTO LIFE mycareers.pk TAHIR HABIB ANFAL ACADEMY PREFACE Biology is a natural science concerned with the study of life and living organisms including their function , Structure , growth , evolution , distribution , identification and Taxonomy. Modern Biology is vast and eclectic field composed of many branches and sub disciplines. ‘ Biology is the most powerful technology ever created. DNA is software, protein are hardware, cells are factories.’ -- Arvind Gupta This brief book can be used by teachers and students in Biology field Specially this book is meant for students of S.S.T , SDO Wildlife , Matriculation F.Sc, B.Sc., B.S(Hons.) of biological group. Students appearing in exams of S.S.T Science in Education department may be immensely benefited by this book. This book has been written strictly according to syllabus of H.E.C. It is copied from different sources mostly from Zoology of Miller and Harley, and extra material is also included. I am highly thankful to my Friends Shahnawaz Silachi & Abdul Hameed Korai . who means a lot for me because their inspiration always remained encouraging for me. mycareers.pkI am also thankful to Mr. Adnan Jaskani C.E.O of Anfal Academy I dedicate my this brief book to Students of Anfal and every student of Balochistan .I am sure this book will prove to be an invaluable asset for the students and teachers. To enhance your concept in Biology please study 1: Campbell Biology By Jane B Reece 2: Biology By Raven & Johnson 3: Zoology by Miller and Harley 4: Integrated principles of Zoology by Hickman 5: Biology by P.S Verma and Agarwal, and study three Books A.B.C Zoology and Botany for B.Sc.
    [Show full text]
  • Divisions of Embryology
    DivisionsDivisions ofof embryologyembryology GeneralGeneral eembryologymbryology Gametogenesis: conversion of germ cells into male and female gametes 1st week of development: ovulation to implantation 2nd week of development: bilaminar germ disc 3rd week of development: trilaminar germ disc 3rd to 8th week: embryonic period 3rd month to birth: fetus and placenta SpecialSpecial eembryologymbryology Skeletal system Cardiovascular system Respiratory syste m Nervous system, etc …. systems GASTRULATION (Gr., belly ) BBilaminarilaminar diskdisk →→ trilaminartrilaminar diskdisk TheThe embryoembryo hashas reachedreached aa pointpoint ofof balancebalance inin itsits efeffortsforts toto :: draw nourishment from the mother (trophoblast layers and their derivatives) to be protected against cellular assault (several ensheathing layers & protective cavities) to harbor enough of its own food (secondary yolk sac ) TimeTime toto movemove –– thethe innerinner cellcell massmass derivativesderivatives differentiatedifferentiate intointo thethe threethree functionalfunctional cellcell layerslayers ofof lifelife outer layer → protective and sensitive inner layer → energy -absorbing connective layer between them → contractile movement GastrulationGastrulation startsstarts withwith primitiveprimitive streakstreak cut trophoblast 90 ° rotation PrimitivePrimitive streakstreak –– dayday 1414 Formed by cells of the epiblast which choose one of the two fates: pass deep to the epiblast layer to form the populations of cells within the embryo
    [Show full text]
  • Developmental Stages in Human Embryos
    DEVELOPMENTAL STAGES IN HUMAN EMBRYOS DEVELOPMENTAL STAGES IN HUMAN EMBRYOS Including a Revision of Streeter's ''Horizons" and a Survey of the Carnegie Collection RONAN O'RAHILLY and FABIOLA MULLER Carnegie Laboratories of Embryology, California Primate Research Center, and Departments of Human Anatomy and Neurolog}', University of California, Davis CARNEGIE INSTITUTION OF WASHINGTON PUBLICATION 63T 198"7 Library of Congress Catalog Card Number 87-070669 International Standard Book Number 0-87279-666-3 Composition by Harper Graphics, Waldorf, Maryland Printing by Meriden-Stinehour Press, Meriden, Connecticut Copyright © 1987, Carnegie Institution of Washington Dem Andenken von Wilhelm His, dem Alter en, der vor hundert Jahren die Embryologie des Menschen einfuhrte und dem seines Protege, Franklin P. Mall, dem Begrunder der Carnegie Collection. Wilhelm His, 1831-1904 Fr.mkhn P. Mall, 1862-191" George L Streeter, 1873-1948 PREFACE During the past one hundred years of human embryology, three land- marks have been published: the Anatomie der menschlichen Embryonen of His (1880-1885), the Manual of Human Embryology by Keibel and Mall (1910-1912), and Streeter's Developmental Horizons in Human Embryos (1942-1957, completed by Heuser and Corner). Now that all three milestone volumes are out of print as well as in need of revision, it seems opportune to issue an updated study of the staged human embryo. The objectives of this monograph are to provide a reasonably detailed morphological account of the human embryo (i.e., the first eight weeks of development), a formal classification into developmental stages, a catalogue of the preparations in the Carnegie Collection, and a reference guide to important specimens in other laboratories.
    [Show full text]
  • Trilaminar Germ Disc
    Contents part one General Embryology ........................................... 1 chapter 1 Gametogenesis: Conversion of Germ Cells Into Male and Female Gametes ..... ..................................................... 3 chapter 2 First Week of Development: Ovulation to Implantation ............ ....... 31 chapter 3 Second Week of Development: Bilaminar Germ Disc ............ .......... 51 chapter 4 Third Week of Development: Trilaminar Germ Disc ............. .......... 65 chapter 5 Third to Eighth Week: The Embryonic Period ............... ................ 87 chapter 6 Third Month to Birth: The Fetus and Placenta ................... ............ 117 chapter 7 Birth Defects and Prenatal Diagnosis ................... ..................... 149 part two Special Embryology ............................................ 169 chapter 8 Skeletal System ............................. ..................................... 171 ix x Contents chapter 9 Muscular System ........................... ..................................... 199 chapter 10 Body Cavities ............................ ........................................ 211 chapter 11 Cardiovascular System ......................... ................................ 223 chapter 12 Respiratory System ........................... .................................. 275 chapter 13 Digestive System ........................... ..................................... 285 chapter 14 Urogenital System .......................... .................................... 321 chapter 15 Head and Neck ...........................
    [Show full text]
  • Embryology of Chick
    EMBRYOLOGY OF CHICK The fully formed and freshly laid hen's egg is large. It is 3cm. in diameter and 5cm. in length. It contains enarmous amount of yolk. Such egg is called macrolecithal egg. The egg is oval in shape. The ovum contains a nucleus. It is covered by yolk free cytoplasm. It is 3mm. in diameter. It is seen on the animal pole. The entire egg is filled with yolk. This yolk has alternative layers of yellow and white layers. They are arranged concentrically around a flask shaped structure called latebra. Below the blastodisc the neck of latebra expands. This is called nucleus of pander. Yellow yolk got its colour because of carotenoids White yolk layers are thin and yellow yolk layers are thick. Yolk is a liquid. It contains 49% water and 33% phospholipids 18% proteins, vitamins, carbohydrates are present. The entire ovum is covered by plasma membrane. It is called plasmalemma. It is lipoprotein layer. This is ovum is covered by egg membranes. Primary membranes: These membranes develop between oocyte and follicle. The primary membranes are secreted by follicle cells. It is called vitelline, membrane is come from two origins. Inner part is produced by ovary. Outer part is from the falopian tube. Secondary membranes: Oviduct secretes secondary membranes. Above vitelline membrane albumen is present. It is white in colour and it contains water and proteins. The outer layer of albumen is thin. It is called thin albumen. The middle layer of albumen is thick. It is called thick albumen, or dense albumen. The inner most albumen is very thick.
    [Show full text]
  • Third Week of Development
    Third Week of Development Trilaminar germ disc GASTRULATION Gastrulation = 3 germ layers formation in 3th week Ectoderm Mesoderm Endoderm GASTRULATION primitive streak formation (on the epiblast surface) in a 15- to 16-day embryo primitive node = in Cranial end / that surround primitive pit Primitive pit GASTRULATION epiblast Cells migration (Invagination) Cell migration and specification are controlled by fibroblast growth factor 8 (FGF8), which is synthesized by streak cells themselves fibroblast growth factor 8 (FGF8), controls cell movement by downregulating E-cadherin,a protein that normally binds epiblast cells together FGF8 then controls cell specification into the mesoderm by regulating Brachyury (T) expression GASTRULATION cells displace the hypoblast (endoderm) Cells lie between epiblast & endoderm (mesoderm) Cells remaining in the epiblast (ectoderm) GASTRULATION cell movement between epiblast & hypoblast layers Cells spread laterally & cranially Cells migrate beyond the margin of the disc Cells contact with the extraembryonic mesoderm covering the yolk sac and amnion GASTRULATION Mesoderm Cells pass the prechordal plate = Is located between the tip of the notochord and the oropharyngeal membrane And is derived from some of the first cells that migrate through the node in the midline and move in a cephalic direction prechordal plate (induction of the forebrain) The oropharyngeal membrane ( ectoderm + endoderm ) Notochord formation Prenotochordal cells move forward cranially in the midline & reach the prechordal
    [Show full text]