A COMPARATIVE STUDY OF THE MORPHOLOGY, HISTOLOGY AND PROBABLE FUNCTIONS OF THE PYLORIC CZECA* IN INDIAN FISHES, TOGETHER WITH A -DISCUSSION ON THEIR HOMOLOGYt BY M. RAHIMULLAH (QURAISHI), M.Sc. (OSMANIA), F.Z.S. [Fisheries OJflcer, H. E. H. the Nizam's Government, lfyderabad (Deccan)] Received May 23, 1944 (Communicated by Prof. Dr. A. Subba Rau, M.A., o.sc., F.A.SC.) (With 28 Text-Figures, and Plates I-1V) CONTENTS PAGES 1. INTRODUCTION .......... 1 2. HISTORICAL REVIEW .......... 2 3. MATErnALAND TECn'NIQtJE ........ 3 4. MORPHOt.OGY OF THE PYLORIC C~ECA IN Theraponjarbua (FORSK.) AS A TYPE .......... 4 5. COMPARATIVE ANATOMY OF rUE C/ECA IN VARIOUS GROUPS or INDIAN TELEOSTS .......... 6. COMPARATIVE STUDY OF THE HISTOLOGY OF THE PYLORIC C~CA ............ !6 . PHYSIOLOGY OF THE PYLORIC C/ECA .. 20 8. DISCUSSION ........ 25 9. SUMMARY AND GENERAL CONCLUSIONS .. 30 10. ACKNOWLEDGMENTS ...... 32 11. REFERENCES TO LITERATURE .... 32 12. EXPLANATION OF PHOTOMICROGRAPHS .. 36 13. KEY TO LETTERING ...... 37 l. INTRODUCTION REFERENCES to literature reveal the fact that while a fairly good account of the morphology of the pyloric cmca has been given in the case of European * The old term 'pyloric c~ca' is being retained in all the pages here for the sake of convenience, though actually these structures arise from the proximal portion of the duodenum. t Revised and abridged version of the Thesis approved for the Degree of Doctor of Science in the University of Madras. B1 1 M. Rahimullah (Quraishi) and other foreign fishes as dealt with in Handbuch der vergleichenden Anatomie der Wirbeltiere, Vol. III (1937), there is very little systematic account of the comparative anatomy, histology, etc., of these interesting structures in the Indian fishes. Furthermore, as regards our present knowledge of the alirnentary tract of fishes in general, very little is known about its histology and that of other structures directly connected with it, and it is for this reason that the author has taken up the present investigation with a view to work out and to present his results in as complete and systematic a manner as possible. A large number of Indian fishes, 119 species in all, included under 50 different families (both fresh-water and marine) have been investi- gated. In order to minimise the cost of publication and the paper, the original thesis has been considerably boiled down, though maintaining the salient features and continuity, and for the present purpose many text-figures and the photomicrographs have also been cut down. 2. HISTORICAL REVIEW The structure (and to some extent the physiology) of the pyloric c~eea has been described by a number of workers, amongst whom the most notable ones are Rosenthal (1824), Hyrtl (1864), Blanchard (1882), Stirling (1884), Macallum (1886), Bonduoy (1897--1899), Gulland (,1898), Johnson (1907), Greene (1912), Kostanecki (1913), Crofts (1925), and Ben Dawes (1930), but the best and most up-to-date works on this subject are those of Jacob- shagen, Pernkopf and Lehner described in the Handbuch d. vergleich. Anat. d. Wirbelt., Vol. 3: 1937. Rosenthal just mentioned the existence of the right and left bunches of the c~eca (2-4 in number) in the sword-fish (Xiphias gladius) without giving any figure. Hyrtl described a very peculiar and interesting case of the dis- position and opening of the "ductus choledoehus" (bile-duct) directly into the "Appendix pylorica" in Fistularia tabacaria Linn. (one caecum), Aulostoma chinese (2 e~eca) and Acanthurus schal C.V. (6 caeca), which has so far not been observed in any other fish--in the last two species of fishes the bile-duct opens into one of the c~eca mentioned. Krukenbe~, Blanchard, Stifling and Macallum have studied the physiological aspect of the pylorie carca. A fairly good morpholo~eal and histological account has been given by a very few workers, viz., Gulland in the case of the Atlantic salmon (Salmo salar); Greene in his description of the king salmon (Oncorhynchus tschawytscha); Kostanecki dealing with fife morphology and homology of the pylorie c~eea as compared with those of other vertebrates; and Ben Dawes on his work on the hostology of the alimentary tract of the plaice (Pleuronectes platessa). The only valuable work on the anatomy and Morphology, Histology & Probable Functions o/'Pyloric Caeca 3 histology of the alimentary canal of Indian fishes that I am aware of is the one on Otolithus ruber (B1. Schn.) by Dharmar@in (Proc. Ind. Sci. Cong., 1936) and the other on Therapon quadrilineatus by Panicker (in MS.)--both from the Research Zoological Laboratories at Madras. Sarbahi, D. S., has also worked out the Morphology and Histology of the Alimentary Canal of Labeo rohita (Hamilton) in detail (Journ. Roy. As. Soc. of Ben,~al, 1940). Mention may be made of Vanajakshi's interesting paper on the Histology of the Digestive Tract of Saceobranehus fossilis and Macrones vittatus (Proc. Ind. Acad. Sci., 1938). On the other hand, Johnson has shown that the pyloric c~eca exhibit what might be called an "individuality" of structure and variation existing in one and the same family (c:[. the family Centrarchid0e ~vhich he has dealt with), while the work of Miss Crofts on an allied topic, viz., on the c~ecal gland (" c~ecal appendage" or "appendix digitiformis ") of Selachian fisbes and its homology, etc., is extremely interesting. 3. MATERIALAND TECHNIQUE Live fishes were obtained for fixation of material, and the pyloric cmca were thus fixed in fi-esh condition, which was necessary for a successful study of the finest histological details of these structmes. Bouin's fluid and other fixatives such as Zenker's and Mann's fluids, etc., were used throughout the work, the first amongst these gave the best results. For all ordinary morphological work, either the whole fish, if it was small (and in that case with the abdomen slightly opened ou0, or the py!oric cama together with some part of the alimentary canal dissected out when the fish was large, was fixed in 6~ formalin. Furthermore, in certain cases, in order to ensure perfect fixation and preservation, the caeca were first of all injected, through the o~sophagus, with Bouin's fluid until they were just turgid after suitaNe ligatures. The c~eca and a small length of the associated gut were then removed and pre- served in the same fluid for 6-18 hours. After carefully separating the c~ca from the surrounding tissues, each, as a rule, if it was a large one, was divided at least into two portions, riz., a proximal and a distal (except in the case of such forms as the Mastacembelid~ in which the two caeca are relatively very small and they are very closely situated too). Each portion of the cmcum (and in certain cases a small portion of the intestine also) was imbedded separately in paraffin, and serial sex'tions (both transverse and longitudinal, 6/~ in thickness) were cut, Sections were variously stained, such as, for instance, in Borax carmine counterstained with Picro-indigo-carmine; Mallory's triple; Heidenhain's iron ha~motoxylin; Mason's iron h~motoxylin method coupled with Acid 4 M. Rahimullah (Quraishi) fuchsin and Aniline blue; Heidenhain's Azan stain; Pasini's method following treatment with strong Delafield's h~matoxytin, and mordanting the sections with 2% Phosphotungstic acid, and then lastly staining with Unna's Wasserblau-Orcein and Giemsa's stain. Sections were carefully studied with compensating oculars ( x 10, • 15 and • 7) in combination with apochromatic objectives (such as 1/12, 40 and 90 with iris diaphragm and numerical aperture 1.25 for oil-immersion purposes). A series of photomicrographs, with both high (including oil-immersion) and low powers, have been taken and then enlarged, and, in addition, many free-hand and camera lucida drawings have also been made and compared. For the detection of cilia in active condition intra-vital staining methods by methylene blue and neutral red were also applied with successful results. 4. MORPnOIX)GYOF "I~E PZLOR~C Ca/CA IN Theraponjarbua (FORSK.) AS A TYPE The pyloric c~ca vary considerably in their number, form, size and arrangement, and constitute a characteristic feature of the intestinal tract of a very large number of families of fishes (both fresh-water and marine), wickly distributed in all parts of the world. For the sake of convenience, I shall briefly describe first the condition of the c~eca as they exist in a common marine fish, Theraponjarbua (Forsk.) (Faro. Theraponid~e), and shall after- wards present a comparative account of them in other groups of fishes invostigat~d by me. TEx'r-Fto. 1.--(a) Dissection of the viscera from ventral aspect of Therapon jarbua showing the cw.ca in situ (• 1). (b) Alimentary canal of the same fish unravelled showing the disposition pf the caeca (• 189 Morphology, Histology & Probable Functions o[ Pyloric Cwca 5 In Therapon ]arbua [Text-Fig. 1 (a) and (b)] there are 10 distinct, tubular (finger-like) c~eca arranged in two bunches of 5 each, and each e~cum opening independently into the duodenum immediately behind the pylorus. In a fish measuring 9.8 era. in length, the average lengths of the whole of the alimentary canal (including the oesophagus, stomach and intestine) and the c~eca were 12.2 cm. and -9 cm. respectively, and the average length ratio of the c~ecum : intestine alone being 1 : 11 (taking the length of.c,~um as a unit). The average breadth of the intestine and that of the c~ca in this fish was 4 mm. The blood-supply 1 of the c~eea is as follows :-- (a) Arterial.--There is no separate cecal artery, but one of the branches of the c~eliaco-mesenterie artery distributes blood to the c~eca, as is the ease in most fishes.