344 KOREN AND DANIELSSEN ON THE 



sought to detach itself from the common mass — and having, 

 at length, after many fruitless attempts, succeeded in so doing, 

 it immediately began to rotate upon itself. We have, in this 

 manner, observed all the individuals of a conglomerate, be- 

 coming detached and separated, one after the other, and when 

 all the embryos were developed, the mass had totally disappeared. 

 It would seem that in this animal, as in the Buccinum, the 

 number of ova which are grouped together to form the future 

 embryo is altogether variable and fortuitous, for not only is there 

 no discoverable law regulating their union, but these conglome- 

 rates are constituted by very different numbers of ova. Thus 

 we have observed in the same capsule some embryos resulting 

 from the union of three or four ova, while sixty or more, had 

 contributed to form most of the others. The different size of 

 the individuals depended on the same cause. This difference of 

 size was very considerable, for we observed swimming in the 

 liquid contained in the capsule, some embryos of I miUim. in 

 diameter, and others of as much as 1^ millim. The number of 

 the embryos in a given capsule varied as much as their size ; — 

 depending in the same manner on the greater or less number of 

 the ova which had united to form each individual. On the 

 average we found from twenty to forty, rarely more. 



Having now become acquainted with the mode of formation 

 of the embryo in Purpura lapillus, let us turn to another phae- 

 nomenon, one of the most surprising which is to be met with in 

 the development of this moUusk, and which will help to explain 

 the singularity in the development of Buccinum, to which we 

 have already referred. It will be remembered that in the latter 

 animal, many of the ova took no share in the act of conglomera- 

 tion (probably in consequence of accidental obstacles), and that 

 their ova soon died, or rather became developed in an excessively 

 incomplete manner. Something similar occurs in Purpura; 

 and as we have had better opportunities for observing this pecu- 

 liarity in the latter moUusk, we are enabled to give a fuller ac- 

 count of it. We have alw^ays found in each capsule an ovum 

 undergoing all stages of cleavage, and which was composed, 

 until the end, of a peripheral layer of clear, and a central mass 

 of dark cells (figs. 10 & 11). A membrane then became rapidly 

 developed around the yelk, and acquired exceedingly fine cilia ; 

 at the upper part of the peripheral layer there were also visible 



