204 
ih: 
12. 
13. 
14. 
15. 
16. 
1 
BULLETIN OF THE 
The basement membrane is a cuticula produced by the inner ends of 
the hypodermal cells. The preretinal membrane is the united 
basement membranes of the lentigen and retina. It may or may. 
not contain mesodermic elements. The sclera is the basement 
membrane of the post-retina. It is usually overlaid with a deli- 
cate mesodermic tissue. 
The lateral eyes are monostichous, and arise from a simple thickening 
and depression of the hypodermis. 
A ring of“ perineural” cells, forming the margin of the depression, 
secretes the lens, and therefore constitutes the lentigen. Since, 
owing to subsequent recession, they do not remain interposed 
between the lens and retina, they have not the double function 
of lentigen and “ vitreous” which the outer layer of the median 
eye has. 
The lens has the same structure as in the median eye. 
The retinal cells occupy only the deeper portion of the depression. 
There are no interneural cells. Along the external portion of 
each retinal cell its lateral walls are thickened into rhabdomeres. 
The nucleus is near the deep end of the cell, and from this end 
the nerve-fibre emerges. Phaospheres are not present. 
The basement membrane (sclera) contains no mesodermic elements. 
There is no preretinal membrane. 
The lateral eyes may be fairly taken to represent the ancestral type 
of the median eyes. 
CaMBRIDGE, July 1, 1887. 
