140 REPORT 1860. 



Danielssen, though wrong as to Purpura, might still be quite correct in the case of 

 Buccinum, and I was very anxious to repeat their observations. It could not be 

 denied that it was a priori probable that what was true of Purpura, would also 

 apply to Buccinum. Still, if I had any bias, it was in favour of MM. Koren and 

 Danielssen. Many insects present us with a case in many respects parallel. In 

 Lepidoptera, Hymenoptera, Diptera, Neuroptera, and the Geodephagous beetles, 

 each egg is accompanied by several vitelligenous cells, or as we might call them in 

 the words of Dr. Carpenter, yolk-spheres. After a while the walls of the vitelli- 

 genous cells disappear, and the whole group unites to form an egg. Here we have 

 undoubtedly a certain similarity with that which, according to MM. Koren and 

 Danielssen, occurs in Purpura and Buccinum. 



Buccinum undatum has been stated* to lay its eggs from the beginning of January 

 to the end of April. On our south coast of England, however, it begins earlier, for 

 I found some fresh ones at Brighton last November. I was not then able to examine 

 them with much care, but in February last I received from Mr. Lloyd two packets 

 of egg-capsules, iu which I have succeeded in tracing the development of the 

 embryos. 



"When I received them, the germinal vesicle had already disappeared, and the 

 eggs consisted of yelk-particles immersed in a viscid substance. According to 

 MM. Koren and Danielssen, each egg is surrounded by a chorion and a vitelline 

 membrane, but I was as little able in the case of Buccinum, as Dr. Carpenter was in 

 that of Purpura, to discover any trace of these structures; and I think I can safely say, 

 from the appearance of the eggs, and from their behaviour when crushed, that they 

 were surrounded by no definite membrane. Many of the eggs, indeed, resembled 

 MM. Koren and Danielssen's fig. 16 (Ann. des Sc. Xat. 1852, vol. xviii.), in which 

 a thick outer membrane is apparently present ; but this arises, as will be presently 

 described, from a condensation of the yelk-particles leaving a clear border of the 

 viscid substance. 



The presence of a vitelline membrane certainly seems to me improbable, but 

 about the so-called chorion I am more doubtful. MM. Koren and Danielssen men- 

 tion (I. c. p. 258) that it early disappears, and this may have already taken place 

 in my specimens as well as in those of Dr. Carpenter. 



The eggs in my egg-capsules did not coalesce. They collected certainly in a heap, 

 but they remained quite separate from one another, and showed no tendency to unite. 



Very few showed any trace of segmentation. In this respect my observations, 

 so far as they go, are quite in accordance with those of MM. Koren and Danielssen. 

 There is, however, always a certain amount of suspicion attached to negative evi- 

 dence, and it seems a priori very improbable that Purpura and Buccinum, which 

 agree so closely in most points connected with their embryology, shoidd differ in 

 such an important matter. 



Dr. Carpenter considers that the capsules of Purpura contain two sorts of egg- 

 like bodies, which, however, can be distinguished from one another only by their 

 modes of segmentation. 



I was not able to perceive any difference in the eggs of Buccinum, except that in 

 some the yolk-granules were condensed, so as to leave a margin of the clear, glaiiy 

 substance ; but it must be remembered that in each capside only a very few eggs 

 undergo segmentation at one time ; .and the process appears to be altogether so 

 irregular, that my observations do not enable me to come to any satisfactory con- 

 clusion on this point. It would be desirable to investigate the formation of the 

 eggs in the ovary, both of Buccinum and Purpura, in order to determine whether 

 or no they are all originally alike, and if not, to determine the points of difference. 



It would also be well worth while to ascertain the relation which the segmenta- 

 tion of the yolk bears to the development of the embryo. 



It is so generally present throughout the animal, and apparently so universal in 

 the Mollusca, that strong evidence woidd be required to show that Buccinum forms 

 any exception to the general rule ; and yet, as far as my observations went, the 

 process certainly seemed to be subject to considerable irregularities. 



The whole subject of yolk-segmentation is one of great interest. 



Among the Entozoa, it appears to occur in certain species of Stronyylus, Ascaris, 

 Gordius, Mermis, and Echinorlvjnchus, and in Filaria, Filaroides, and Sphceru/uriu. 



* Ann. des Sc. Nat. I, c. p. 258. 



