24 
Dr. Carpenter, on the Development of 
having no definite form, and nearly filling the ovigerous 
capsule.* 
I am not able to detail, as fully as I could wish, the mode 
in which the segmentation proceeds in the true ova, and in 
which the proper embryonic structures first appear ; but as far 
as I have been able to gather from my own observations and 
those of Mr. Busk, the subdivision of the smaller of the two 
primary segments (which I shall call the anterior) takes place, 
until a collection of very minute spheres is formed along one 
margin of the larger or posterior segment which has undergone 
no subdivision (Plate III., fig. 6, />, c). This portion then 
becomes pellucid, and is obviously bordered by a membrane 
(fig. 8, d) ; and gradually a pellucid margin is seen to present 
itself around the whole vitellus (fig. 8, a, 5, c), the border, 
however, being still much broader at the anterior part than at 
any other. The pellucid membrane soon becomes clothed 
with very delicate cilia ; and these are particularly abundant 
at its anterior extremity, where an important change speedily 
takes place. The broad margin extends itself on either side, so 
as to form the rudiments of the two ciliated lobes which seem 
to belong to the early embryos of all Gasteropods (fig. 8, c) ; 
whilst between these, the transparent envelope seems to thin- 
away (?), until an aperture is formed, leading directly down to 
the cavity wherein the vitellus lies (fig. 8, d). This aperture 
elongates into a canal, the whole interior of which, as well as 
its margin, is thickly clothed with cilia (fig. 9, «, h). Thus 
the larval Purpura becomes possessed, by such a process of 
transformation as takes place in the embryo Polyzoon, of a 
mouth with ciliated lobes on either side, a ciliated oesophagus, 
and a gastric cavity ; which, although at first fully occupied by 
the original vitellus, soon shows a capacity for more, the walls 
of the cavity itself being enlarged by material withdrawn from 
the vitellus, and the space occupied by the latter being cor- 
respondingly reduced by the appropriation. 
This process is going-on at the same time with the segmen- 
tation and coalescence of the vitelline spheres. But there 
is no such relation between them, as binds them to an 
exact synchronism. For I have sometimes met with a 
dozen or more of embryos, developed up to the oesophageal 
stage, in a capsule whose vitelline spheres had not yet begun 
* Notwithstanding the most careful examination, I must confess myself 
unable to discover in the conglomerate mass, still less in the bodies of the 
embryos which are formed at its expense, those distinct indications of the 
original clusters, which are represented by MM. Koren and Danielssen 
in their figs, 27 — 31 ; and since the vitellus is swallowed by the embryo 
(p. 25), particle by particle, it is impossible that any such grouping can 
be preserved within their bodies. 
