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The Development of Amphibola Crenata (Martyn)

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The Development of Amphibola Crenata (Martyn) The Development of Amphibola crenata (Martyn). By Winifred Clieyne Faruie, M.A., Geraldine, New Zealand. With 13 Text-figures. IN 1919 I gave an account of the general anatomy of this interesting New Zealand littoral Pulmonate, and in the course of that account showed that the genital duct is single ; it extends from ovotestis to genital pore in one undivided canal; in other words the different structures identified by Quoy and Gaimard, and by Hutton respectively, as oviduct do not exist.1 At the time when that article was published I was not in a position to state how the eggs were conveyed to the exterior, and proposed to gather material month by month till the date of egg-laying was determined and their method of passage was ascertained. As a result of numerous observations extending over two years I am now able to satisfy myself on these two points : (1) That the egg-cells descend by way of the hermaphrodite duct through the coiled non-glandular portion of the common duct. x On p. 84 I wrote : ' Sections across the right side of the body show no trace of a duct between the rectum and the genital duct, whereas sections across the genital duct itself show the existence of a deep fold in its wall, which serves to divide the duct into two portions, presumably, during the passage of the ova and spermatozoa.' I cut serial sections again across the same region when the animal was engaged in laying eggs, but with the same negative result: I can, therefore, only come to the conclusion that a distinct and separate oviduct does not exist, though unfortunately I was not able to detect ova actually in the lower region of the common duct. 454 WINIFRED CHEYNE FARNIE (2) That the eggs, embedded in an albuminous coat and an egg-membrane or shell, leave the body by the genital pore below the right tentacle. But unfortunately I have been unable to trace their descent along the lower portion of the common duct, or to find the place of formation of the egg-membrane or shell. The series of observations had to come to an end, for I left Dunedin in order to take up a position in an inland school. f The work was carried out in the Biological Laboratory of the University of Otago, and I owe my thanks to Professor Benham for the interest he took in my work and for many helpful suggestions. SUMMARY. The development was traced out day by day, though details of later steps of cleavage and gastrulation were not studied : the formation of the trochosphere and veliger were, however, carefully followed out. Unlike what occurs in the majority of Pulmonates, the veliger stage is typically and well developed ; the trochosphere phase, on the contrary, is somewhat abbre- viated. The shell-gland is not formed by an invagination, but is represented merely by a thickening of the epidermis. The veliger escapes from the egg-mass by the action of the operculmn, the edge of which is used to bore through the egg- shell and surrounding jelly. It leads a free life ; but I was unable to keep the larva in captivity for more than one day after hatching. During this time it swims actively, coming to rest from time to time with its velar lobes downwards. 1. THE EGG. So far as I can ascertain nothing is known as to the develop- ment of Amphibola. For two years I made a series of monthly observations to discover at what period the discharge of the eggs occurs and where development takes place. The ova are fully formed in the hermaphrodite gland at the beginning of November, two or three weeks after the first DEVELOPMENT OF AMPHIBOLA 455 appearance of fully developed spermatozoa. After being discharged into the hermaphrodite duct they remain a short while in the slight enlargement at the junction of the seminal vesicle and the main duct. Self-fertilization probably takes place here as the seminal vesicle at this period contains live spermatozoa in active motion. I have found the ova passing through the coiled glandular portion of the common duct into the non-glandular portion. In the pouch at the commence- ment of the non-glandular portion, which contains secretion from the albumen gland, albumen is deposited around each egg. Unfortunately I have been unable to trace the course of the ova any further in the animal, and it is only on two TEXT-FIO. l. Egg-nidus (natural size). occasions out of many scores of observations that I have been able to trace their course as far as the non-glandular portion of the common duct. On one of these occasions, from a microscopical preparation of a freshly dissected specimen in salt solution, I observed several ova passing along the glandular portion of the common duct, during which the ova were con- stricted as they were forced round the several coils. This duct is thickly ciliated, so that, though it is extremely con- voluted, the ova did not take long to pass along it. I have been unable to ascertain where the shell is deposited. On November 3, 1919, I picked up on the mud-flats a ribbon- shaped, concavo-convex mass of sand particles (Text-fig. 1) lying quite by itself, the concave surface being next to the ground. It was an egg-nidus, for examination proved it to 456 WINIFRED CHEYNE FARNIE contain masses of eggs embedded amongst sand and particles of mud held together by gelatinous material. The band is about 80 mm. in length and about 10 mm. across ; it is curved in itself, so as to describe rather more than a circle, one end over-passing the other. In other cases the two ends just meet. It is similar in appearance and structure to that of Natica, TEXT-PIG. 2. View of an egg with its albumen, shell-membrane, and gelatinous envelope. (Much enlarged.) EXPLANATION OF TEXT-FIGURES 2-13. The following lettering is used throughout, alb., albumen of egg ; b., blastopore ; b.c, bodj'-cavity of larva ; b.w., body-wall; e.g., cerebral ganglion ; d.gl., digestive gland ; ent., enteron; /., foot; g., groove in mantle indicating the probable position of anus ; g.e., gelatinous envelope ; int., intestine ; k., kidney; k.c, central cell of kidney ; k.d., kidney duct; m., mouth; mac, macromeres ; m.e., mantle edge ; roic, micromeres ; m.s., mesoblastic strands ; n., nucleus of ovum or its position ; o., ovum ; oe., oesophagus ; op., operculum ; ot., otocyst ; pig.c, pigment cells in velum ; pig.in., pigment mass, perhaps repre- senting the future tentacles ; p.g-, pedal ganglia ; sh., shell of larva ; sJi.gl., shell-gland ; sh.m., shell-membrane of egg ; St., stomach ; v., velum ; vis., visceral mass of larva ; v.m., velar muscle ; y., yolk-granules. but that of the latter is considerably larger, and is found in clear sand facing the open sea. The only Gastropoda found on these rnud-flats were Arnphibola, Patella, Siphonaria, Oncidiuni, and Chiton. It is known that Patella lays its eggs in masses surrounded by jelly, during September and October. DEVELOPMENT OF AMPHIBOLA 457 Siphonaria forms clear, gelatinous, ribbon-like masses with several eggs in each capsule. Oncidium masses its eggs in numbers to form gelatinous balls, and Chiton lays its eggs freely in water and the egg- shell is spiny. Since the nidus agreed with none of these descriptions as- given by Korschelt and Heider (1900) I concluded it must be that of Amphibola. Up till this time I had not traced the course of the ova through the common duct, and had no idea what the fully formed ova were like. Later I found similar egg-ribbons in association with Amphibola in such positions as to lead to the conclusion that the animals had just formed them. The chances were that I might find ova still in the common duct of such specimens, and thus be able to discover where the shell was deposited ; but as no ova were visible in the duct on examination, I con- cluded that the animals had either not formed these nidi or that they had deposited all their eggs. On every visit made in the forenoon, during the month of November, crowds of Amphibola were seen each close to the end of such an egg-ribbon as if it had recently been formed by the gastropod. But during the afternoon I found no animal in such positions, and as, during the morning, they were associated with none but fully formed nidi, I concluded that the eggs must be deposited during the very early hours of the morning only. Judging from the length of the nidus we would expect the eggs at either end to be in different stages of cleavage, but in only a few cases was this so ; for instance some of the eggs exhibited division into two, but most were still unseg- mented. This seems to agree with Korschelt and Heider's (1900) statement for Pulmonates that cleavage begins two hours after the egg is laid. On November 23, three weeks after examining the first nidus, a microscopical preparation of the glandular portion of the common duct of one specimen showed ova passing along it as described above, and as these ova resembled those already NO. 271 H h 458 WINIFRED CHEYNE FARNIE seen in the nidi I believed that I had conclusive evidence for my original opinion. This was confirmed on November 24, when I actually saw one Amphibola form a nidus in the laboratory in a dish of sea-water and sand.
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