DEVELOPMENT OF THE PECTINIBRANCHIATA. 343 



place. In these ova, 2, 4, 6, 7 > 9, 10, arid even 18, cleavage 

 masses might be counted ; the contents of all were obscure, and 

 without any nucleus, Even at this period, we thought we no- 

 ticed a tendency to agglomerate the ova in the viscous liquid, 

 analogous to that whose effect we observed in Buccinum unda- 

 tum, but it was far from being well marked, and the commencing 

 cleavage threw great obscurity upon what was going on. But all 

 our doubts were completely dissipated on the twelfth day, when 

 the phenomenon which had been exhibited by Buccinum unda- 

 tum was repeated by Purpura lapillus. In fact, the ova were 

 agglomerated and formed a compact mass; the viscous and 

 albuminous liquid had at the same time become as clear as 

 water, and could be separated from the conglomerate with great 

 ease. Examining the latter with attention we observed that it 

 was composed of many groups of various extent and without 

 any determinate form ; these groups, under the microscope, ap- 

 peared to be composed of ova, the greater number of which had 

 undergone cleavage, while others had not (PL XI. fig. 24). 



On the sixteenth day we re-examined many capsules. All the 

 ova were agglomerated, but the conglomerate was a little altered, 

 inasmuch as certain groups had become more distinct, more 

 sharply circumscribed, and projected more from the common 

 mass. Some were cylindrical, others pyriform, but they were 

 all terminated by a peduncle which connected them with the 

 common mass (fig. 27). The microscopical examination of each 

 group showed it to be formed by the union of ova imbedded 

 in a very viscid mass, and invested by a delicate membrane, 

 which soon became covered with very fine cilia (fig. 27). The 

 ova themselves had undergone no further cleavage, and it ap- 

 peared to us that this process had stopped as soon as the agglo- 

 meration commenced. Soon after, we observed a well-marked 

 grayish, semitransparent, finely granular matter, exuding from 

 the sides of the above-mentioned peduncle, and becoming, at a 

 later period, covered with vibratile cilia (the foot) (figs. 26, 27 

 & 28 b}. We also observed a similar mass becoming developed, 

 in the same manner, at the base of the peduncle, and giving 

 origin to two lobes, which afterwards increased and acquired fine 

 cilia at their edges (fig. 7 d). The embryo thus constituted 

 now begins to move a little by the help of its cilia. In fact, it 

 was observed to make feeble efforts in various directions, as if it 



