MUSEUM OF COMPARATIVE ZOOLOGY. 105 
tion of the fibres of the optic nerve in the anterior eye asin Fig. 28. The post-retinal 
nuclei still distinguishable, although considerably flattened. In the posterior eye the - 
retinal cells are separated from the ‘‘lentigen” by a distinct pre-retinal membrane. 
Bacilli already well developed in the anterior half of the eye. The tapetum reaches 
to the external cuticula as well as to the internal cuticula, and contains several tape- 
tal nuclei. The optic nerve and its radiating fibres are shown in the “ post-retinal” 
layer. 
Figs. 25-32. Diagrammatic figures to show a possible course of development of 
the several layers of the simple eyes from the hypodermis. Consult the text, pp. 
87-98. 
Figs. 25, 26, 30-32. To illustrate the development of eyes of the ‘ pre-nuclear ” 
type. The primary bacilli, at the distal ends of the hypodermal cells, are colored yel- 
low ; the secondary bacilli, at the (originally) deep ends of the cells, red. Optic- 
nerve fibres are yellow ; they should have been continued up to the nuclei. Arrows 
in Figs. 30, 31, indicate the directions of the light from two different sources. (The 
letters 4. and P. were accidentally omitted.) 
Figs. 25-29. To illustrate the development of eyes of the ‘‘ post-nuclear” type. 
The primary bacilli (yellow) retained on one side of the eye; replaced on the other 
side by the tapetum (here assumed to have been developed from the remaining half 
of the original retina). Optie-nerve fibres, red; they should have been continued 
up to the nuclei on the side away from the bacilli. 
CONTENDS: 
I. Source AND RELATIONS OF RETINA. PAGE 
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