DEVELOPMENT OF THE CEPHALOPODA. 43 
possible to suppose that at one particular point not hit off in 
the other sections, the layer ym is continued into the cavity 
al, and has there given rise to its lining cells. This I think 
is very unlikely, from the examination of numerous sections, 
though such a derivation at an earlier stage of development 
than those examined by me is not impossible. The layer 
ym agrees in the character of its cells with the Vertebrate 
hypoblast (chick). 
In fig. 5 the ink-sac is seen to commence as a diverticulum, 
2s, of the primitive chamber of the anal tubercle. The epithe- 
lium of the chamber of the anal tubercle is in close contact 
from the earliest stage at which I have seen it, with the 
epidermic epithelium, and much later at this point the anus 
breaks through. I have not found, what might be looked for 
on & priori grounds (comparison with other molluscs), that the 
chamber of the anal tubercle is formed by an invagination from 
the external layer at this point. 
In pursuing further the development of the chamber which 
makes its appearance in the anal tubercle, I found it to 
increase considerably in size, and to extend around the base 
of the internal yelk, where subsequently, by steps which I 
have not followed out so as to enable me to epitomise them 
without reference to many figures, it effects a junction with 
the cesophageal tube which has pushed its way down on the 
opposite (oral) face of the embryo. The whole of the ali- 
mentary canal, with the exception of pharynx and esophagus, 
develops by the growth of this primitive chamber of the anal 
tubercle. In fig. 8 (a little later in age than fig. 5) a 
diagrammatic transverse section is given, showing the first 
development of the liver as two coeca extending from it, so as 
to embrace the cavity occupied by the internal yelk. In fig. 
9 a vertical right-and-left section of a somewhat older embryo 
is given, showing the upward (towards the head) growth of 
the hepatic processes or diverticula. ‘They increase rapidly 
in size, and finally come to occupy exactly the space once 
filled by all the posterior portion of the internal yelk (that is, 
the yelk enclosed by the embryo as distinguished from that 
held in the appended yelk-sac.) 
Blood-vessels and lymph spaces.—In the various sections 
(more than 150 in number) of embryo Loligo, Sepia, and 
Octopus which I have made, the development of the hearts, 
large vessels, and of the renal organ have been followed out. 
Atthe present time I will merely point to the fact, that the 
mass of cells, mes, which we may for convenience call “ meso- 
blast,” splits at various points (see fig. 95, fig. 6, fig. 7, fig. 8, 
pv and v), giving rise to a disconnected series of spaces, 
