DEVELOPMENT OF THE PECTINIBRANCHIATA. 331 



of the ova and from other evidence which we have obtained, it 

 would appear that Buccinum undatum lays its eggs from the 

 beginning of January to the end of April. 



Many oviparous capsules were opened, and their contents 

 subjected to microscopical examination. Each capsule enclosed 

 a limpid pellucid viscous liquid, resembling white of egg; in 

 this viscous humour and at the bottom of the capsule there lay 

 a large number of ova (6-800), which could with difficulty be 

 detached from one another ; each egg was composed of a delicate 

 transparent membrane (chorion), in the interior of which was 

 another, still more delicate, enveloping the yelk. The latter, 

 spherical in shape, was composed of a viscous fluid, in which 

 was dispersed a multitude of rounded granules, variable in size 

 and of a clear yellow colour (PI. X. fig. 2). No trace of either 

 germinal vesicle or germinal spot was visible ; the diameter of 

 the ovum varied between 0'257 and 0*264 of a millimetre. 



On the 8th, 13th, 15th and 20th of March we re-examined 

 capsules of all the racemes ; the ova had remained, to our great 

 astonishment, spherical and without division*. 



On the 24th of March the ova were still undivided, but in- 

 stead of being scattered as before, they had approximated to one 

 another. The chorion had begun to disappear ; the larger por- 

 tion of the yelk was diffused (Detail epanchee), and invested 

 by the viscous albuminous fluid which surrounded the vitelline 

 membrane. Some days afterwards, the ova had become agglo- 

 merated into a single mass, which at its surface was divided into 

 many portions, in which each ovum could be distinguished by 

 the naked eye. In general the number of the ova constituting 

 each of these portions varied from six to sixteen. 



On the 29th of March again, we examined many capsules ; 

 the isolated groups were more sharply defined and each mass 

 had become ovoid or reniform ; it was observable also that these 

 groups were united together. 



On the 1st of April we examined many capsules; one of 

 them enclosed twelve embryos ; they were ovoid or reniform, 

 and provided with two rounded lobes (vela) and a foot (figs. 3. 

 4 c & 5 e.). The fluid contained in this capsule was as clear as 



* We have at times, in a few ova, seen a small conical eminence upon the 

 vitellus. 



