THE DEVELOPMENT OF THE COMPOUND EVE. 551 
therefore, if I am right, corresponds with the vitreous in the 
Vertebrate. 
Multi-nucleate Rhabdomes.—Although the rhabdomes of the 
Blow-fly only exhibit one nucleus in the shaft (Pl. XXXVIII., 
Fig. 1) there is no doubt whatever that in many Arthropods the 
thabdomes are multi-nucleate cells. Grenacher’s figures are 
sufficient evidence of this, and I would draw attention to the 
strong tendency of the parablastic elements of the mesoblast 
to become multi-nucleate. Although I have not been able to 
satisfy myself that this condition is characteristic of any stage 
of development in the Blow-fly, it is very possible that it is. 
Amongst the crowded nuclei at the outer end of each rhabdome 
indicating the pigment cells of the irides and the chamber, it 
is impossible to say that some of these do not lie within the 
great rod; indeed, some appear as if they do. When several 
nuclei exist in one great rod, portions of the original cell may 
become independent cells, as they certainly do in Tipula. 
The Origin of the Pseudo-cone.—The pseudo-cone is formed 
from four cells which appear beneath the cornea. Some 
observers believe these cells are the four sub-corneal cells; this 
is the opinion of Grenacher, but Patten strongly advocates 
the view that they form a second layer of cells beneath the 
sub-corneal cells. I am very much inclined to think they do. 
It appears to me that the sub-corneal cells are converted into 
the corneal lens, and that their shrivelled nuclei persist as four 
minute nuclei, which are always present at the edges of the 
corneal lenses ; I am not, however, in a position to state this 
with certainty. 
The pseudo-cone is undoubtedly formed by the vacuolation 
of four cells, which are not apparent until a late stage of de- 
velopment, and it appears to me possible that these four cells 
are developed from the anterior end of the great rod by the 
separation from it of four nucleated portions of protoplasm. 
If so, then the pseudo-cone, which encloses the anterior end 
of the rhabdome, is also mesoblastic in origin. Certainly the 
cells of the pseudo-cone have nuclei, which are very unlike the 
four sub-corneal nuclei of an earlier stage. 
