44 E. RAY LANKESTER. 
which are the representatives of a cwlom or body-cavity. 
From these and their walls are subsequently developed 
the hemolymph spaces and hemolymph vessels and circu- 
latory organs. 
Development of the Otocysts——I have previously stated 
(loc. cit.) that the auditory capsules commence as open in- 
vaginations of the epidermic layer; I now give a sketch of 
one of these invaginations (fig. 17) at a period when the eye 
and pen-sac are also in the condition of open chambers formed 
by the epidermic layer. 
Development of the Eye—The facts to be stated under 
this head were brought forward in Section D of the British 
Association at its meeting in Belfast in last August. 
The eye first appears as an oval ridge, enclosing an area of 
the same form on the surface of the embryo. It is seen ina 
side view in fig. 12, from above in fig. 13, and in diagram- 
matic section in fig. 15. ‘The walls of this oval area close 
in above, leaving a minute scar at their point of juncture. 
They are seen not quite closed in fig. 14 from above, and in 
section in fig. 16. This phase of the development of the 
Dibranchiate. Cephalopod’s eye corresponds with the perma- 
nent condition in the ‘letrabranchiate Nautilus. In fig. 10 
the eye is seen at a later period and not in strictly median 
section. A mass of mesoblastic cells are now seen to inter- 
vene between the primitive optic chamber and the epidermic 
layer of cells. ‘Lhe lining of the primitive optic chamber is 
entirely derived from the epidermic layer from which it was 
invaginated. ‘The cells of the posterior wall and sides become 
developed into retinal elements, the cells of the anterior wall 
are differently modified, becoming changed into a “ ciliary 
body,” which as Hensen has described is applied to the sides 
of the lens and contains muscular elements. In the section 
fig. 18 these cells are seen, ci. The section is not precisely 
through the median plane ; such a section of the same eye is 
given in fig. 19. ‘The first commencement of the dens is seen 
in these figures. It is apparently a viscid, somewhat fibrous 
structure, totally devoid of cellular elements. It is formed 
entirely within the primitive optic chamber, and at first 
depends as a short cylindrical rod from the middle point of 
the anterior wall of that chamber, that is to say, from the 
point at which the chamber finally closed up. It grows 
subsequently by the deposition of concentric layers of a horny 
materiai around this core. No cells appear to be immediately 
concerned in effecting this deposition, and it must be looked 
upon as an organic concretion, formed from the liquid con- 
tained in the primitive optic chamber. 
