244 
RICHARD ASSHETON. 
here intended between ‘ kephali ’ and ‘ notes ’ is not iden- 
tical with that between head and trunk (trunk segments 
having been ascertained to enter into the composition 
of the head), but that on one side should be ranged the 
very foi’emost portion of the head to which the ophthalmic 
[olfactory?] and optic nerves belong, whereas on the other 
we place the further subdivisions of the brain with their 
cephalic nerves, as also the basis of the skull with the remains 
of the notochord it contains, the visceral arches and the whole 
of the trunk.” 
I am inclined to think that a very considerable part of the 
gut, including the pharynx, and certainly the heart, are proto- 
Text-fig. 3. 
Diagram of a vertebrate to show approximately the parts clue to 
protogenesis and denterogenesis respecdively. a, anterior ; 
d, doi-sal ; p, posterior ; v, ventral suii'aces. 
genetic. But the details of this form a subject for further 
experimental research. 
Then in his paper of last autumn Hubrecht says (p. 43) : 
“ I think we may safely say that by the rapid extension back- 
wards of the differentiation process, . . . the dorsal region 
of the trunk is laid down in outlines (hence the word noto- 
genesis), whereas the derivates of the ventral mesoblast find 
employment in the construction of the posterior and postero- 
ventral portion of the embryo.” 
The ventral mesoblast, by which Hubrecht means the 
mesoblast proliferated from the posterior or ventral lip of the 
blastopore, is, so far as the mesoblast is concerned, the evidence 
of the extent of the effect of deiiterogenesis on the ventral 
