1905.] 



NATURAL SCIENCES OF PHILADELPHIA. 



12^ 



is hatched from the egg and the newly hatched larva shows it clearly; 

 the boundaries of the eye are not as well marked as they become by 

 the time the larva is one day old. The optic ganglia are formed at 

 this time, as they arise very early in the development, but the retinu- 

 lar ganglia are not formed until a- later larval period. 



Fig. 1. — Edge of entire eye, 

 showing the relation of lens to 

 the chitin of the body and the 

 strip of chitin running down 

 into the head around the eye. 



Fig. 2. — Section through edge of pupal 

 eye before infolding occurs, showing transi- 

 tion from hypodermis to eye structures. 



This thickened laj-er of the hypodermis of the newly hatched larva 

 consists of columnar cells with their nuclei arranged at different levels, 

 giving the eye a pseudo-striated appearance. The cells at this time 

 all extend the same distance, so that the eye arises from a strictly one- 

 layered condition. At this time there is no connection with the optic 



