TRANSACTIONS OF THE SECTIONS. 141 



Van Beneden asserts that it occurs in the Cestoids generally ; but this is denied 

 by Kolliker, as far as concerns Tenia and Bothriocephalus. There is a similar differ- 

 ence of opinion as regards Cucullanus elegans, in which species Siebold (misled, 

 according to Kolliker, bv the large size of the two primary embryo cells) supposed 

 that there was a true segmentation. The figure given by Kolliker sufficiently 

 explains how such a mistake might have occurred*. Van Beneden also denies that 

 any segmentation occurs in Echinorhynchus, a difference of opinion which may have 

 arisen from different species having been examined, since, while segmentation has 

 been observed in Ascaris nigrovenosa, acuminata, succisa, osculata, labiata, brevi- 

 caudata, &c, it appears, according to Kolliker, to be absent in Ascaris dentata. It is 

 evident therefore that this species cannot be naturally included in the same genus 

 as the others, and that the two groups, however similar, are in reality very remote 

 from one another. 



Oxyuris ambiqua and Gyrodactylus have been also asserted to develope without 

 volk-seo-meutation, though in the' case of the latter there appears to be some doubt. 

 In the Annelids it has been observed in Polynoe, Exogone, Clepsine, Nephchs, 

 Protula, Hcrmclla, &c, and is not known to be absent in any. 



It has also been observed in the Tardigrada and in Lacmulana. Among the 

 Articulata, it has been noticed in Nicothoe by Van Beneden, in Diaptomus and 

 Cyclops by Claus (which I also can confirm). On the other hand, in Insects t and 

 Dapknia I have sought for it in vain, and it is unmentioned by Rathke and Heroldt 

 in their works on the development of Asellus, Oniscus, Astacus, and the spiders, 

 though in the two latter cases it may perhaps be represented by the dispersion and 

 reunion of the "Keinischeibe." 



Amono- the Mollusca it has been described in Actceon, Aplysia, uEohdia, Dentahum, 

 Boris, Umax, Limruea, Planorbis, Teredo, Tergipes, Tritonia, &c. 

 Among the Bryozoa it occurs in Alcyonella. 



In Salpa it has been observed by Kolliker, while in Pyrosoma it would appear, 

 according to the recent researches of Huxley, to be impossible. 



All this, however, is a digression, and I must return to my Buccinam. 

 The egg-capsules were sent to me on the 19th of February, at which date the eggs 

 in most "of them were diffuse, though in some they had already begun to collect 

 together. At this time no embrvos had appeared. On the 29th the eggs were 

 more closely compacted, and each capsule contained from five to twenty embryos. 

 The eggs now adhered together in a more or less compact mass, but showed 

 no tendency to amalgamate, and were very easily separable from one another by 

 the point of a needle. Imbedded in and about the mass were the embryos; the 

 smallest consisting apparently only of a clear substance, surrounding the almost 

 unaltered yolk, and having oil one side an enormous orifice or mouth leading into 

 a central cavity. The more advanced embryos already showed traces of the ears 

 and the salivary glands, and began to swallow the other eggs whole. In spite of a 

 careful search, I never found any collections of eggs simply surrounded by a mem- 

 brane, as described by MM. Keren and Danielssen and figured, I. c. fig. 17. Embryos 

 containing more than three or four eggs always possessed the salivary glands and 

 auditory organs. Nevertheless, were Messrs. Koren and Danielssen's theory correct, 

 such masses ought to be tolerably frequent. 



Nevertheless, the young embryos were so voracious and swallowed so many other 

 eggs that they became greatly distended, and on a superficial view appeared some- 

 times as in MM. Koren and Danielssen's fig. 17 (Ann. des Sc. Nat. 1852, pi. 5). 

 By turning these over, however, with a little care, the ciliated lobes could always 

 be discovered. At this period also the eggs sometimes adhered together so as to 

 form rounded masses; but in such cases they were quite separate, were surrounded 

 by no membrane, and were easily separable from one another. Nevertheless, if 

 masses such as those described and figured by MM. Koren and Danielssen 

 formed one stage in the normal development, it is very unlikely that I shoidd 

 never have come across a single specimen in this stage. 



Moreover, even in the smallest embryos we see already a broad oesophagus, and 

 * Van Beneden appears also to have fallen into the same error. See Mem. sur les Vers 

 Intestinaux, p. 275, 1858. 



t Leuckart supposed that he had found it in Diptera, but he was doubtless misled by the 

 vitelligenous cells. 



