434 Messrs. Koren and Danielssen on the 



although deposited at the same time and enclosed in the same 

 capsule, nevertheless exhibited a great diversity in the progress 

 of their segmentation. We did not observe any nucleus in the 

 spheres of segmentation. Nordmann did not detect them in 

 Tergipes, Rissoa, and Littorina, We have had the opportunity 

 of observing the little clear body which Dr. Carpenter has seen 

 quitting the egg, and which we had not previously noticed. 

 Some days later in the development, the viscous liquid, which 

 filled the capsules, began to grow more fluid, so that the eggs 

 could be made to escape with the greatest ease ; they were then 

 conglomerated, and apparently formed a compact mass. On 

 examming this more closely it was found to consist of several 

 adherent groups, which were of different sizes, although they 

 had no distinct forms. Under the microscope, these groups 

 proved to consist of eggs, placed one upon the other like 

 a mass of balls, of which the greater number were in different 

 stages of segmentation, whilst others were not. On the six- 

 teenth day the groups had usually become more distinct, more 

 clearly circumscribed, and more detached from the common 

 mass ; they had acquired a cylindrical or pyriform shape. Each 

 of these groups was formed by the union of eggs imbedded in a 

 glutinous mass and covered by a delicate membrane, which was 

 soon furnished with very fine cilia. The eggs themselves had 

 undergone no subsequent segmentation, as the act of progressive 

 segmentation had stopped as soon as the conglomeration was 

 effected. At the side of the upper part where the embryos were 

 attached to the common mass, we could detect an exuded, 

 greyish, semitransparent, and finely granular mass, which had 

 the appearance of increasing the membrane, the outer margins 

 of which began to be furnished with some cirrhi. Whilst the 

 membrane was increasing more and more at the point just 

 mentioned, a similar, yellowish, exuded mass was perceived 

 nearly at its middle; this forms the base of the future foot 

 (PI. XVII. fig. 3 c?). The embryo thus formed began to move 

 a little by the aid of its cilia and of some cirrhi ; it was in 

 fact observed to make feeble efforts in different directions, as if 

 seeking to detach itself from the common mass ; and when at 

 length, after various futile attempts, it succeeded in doing this, 

 it began immediately to turn upon itself. We have seen all the 

 individuals, one after the other, detach themselves and move off 

 in this way, until all the groups had become developed into em- 

 bryos. We may believe that in this animal, as in Buccinuniy the 

 number of eggs which combine to form the future embryo is 

 perfectly fortuitous ; for not only can we discover no rule for 

 this formation, but, moreover, we find that these aggregates are 

 formed of very different numbers of eggs. Thus, in the same 



