DEVELOPMENT OF THE CEPHALOPODA. 45 
From the wall of mesoblast covered with epiblast lying in 
front of the primitive optic chamber after its complete invagi- 
nation a circular fold arises, which is seen in the various 
sections as two flaps marked IF. They are the iris-folds, and 
grow so far towards each other as to partially enclose an 
anterior optic chamber, soc. ‘The complete enclosure of this 
chamber is effected by further overgrowths of tegumentary 
folds, the corneal folds, sometimes called a coalesced eyelid, 
which in many cephalopods completely unite in the middle 
point, so as to form a cornea-like structure, or else leave a 
minute aperture. This tegumentary overgrowth is seen in the 
section fig. 21, marked TO. 
The layer of mesoblastic cells lying between the anterior 
wall of cells of the primitive optic chamber, and the posterior 
wall of epidermic cells (pe) of the secondary optic chamber, 
is large and obvious enough in the younger stages of the 
eye, but it subsequently becomes atrophied, and in later 
stages, figs. 20, 21, is a mere structureless membrane. 
From its position in the eye of the adult Sepia and Loligo 
it appears that the lens must in a later stage of development 
than that drawn in fig. 21 push its way through the median 
anterior area of the primitive optic chamber and project into 
the secondary or anterior optic chamber, where the iridian 
folds he closely upon it. Whether the cellular structures at 
this point are actually broken through, or whether they 
merely atrophy and become adherent to the anterior portion 
of the lens, I am not at present able to say. 
The important result, however, is that the lens is em- 
braced equatorially by the remarkable ciliary body deve- 
loped from the anterior lining cells of the primitive optic 
chamber. 
The identity of the Dibranchiate eye within its earliest 
phase with the adult ‘Tetrabranchiate eye is an important 
result from one point of view. Not less interesting is the 
total divergence of the cuttle-fish’s eye from that of the 
vertebrates m its mode of development, whilst presenting 
so much identity in mechanical arrangements with it. One 
cannot leave these facts without pointing, moreover, to the 
close agreement in development and early structure of the 
Cephalod’s primitive and the Vertebrate’s secondary optic 
vesicle, respectively retina and lens. 
The White Body.—TVhe remarkable history of this body was 
also the subjectof a communication which I made to the British 
Association at Belfast. In the epitome (Joc. cit.) of my earlier 
observations on Loligo I stated that below each eye a deep and 
long invagination of the epidermic layer occurred, giving rise 
