86 Frederick H. Krecker. 



of the head. Of the former an oval pair is on the ventral surface and 

 a circular one on the dorso-lateral surface of the head. 



The accessory eyes have a large circular lens followed by a com- 

 paratively thin layer of corneal hypodermis encircling which is a single 

 row of large iris cells. Below this there is a crescent shaped area of 

 polygonal rods which are terminally situated upon the retinal cells and 

 are separated from one another by a seam of denser material which is 

 enlarged at its basal end. There is no grouping of rods or of retinal 

 cells. From the proximal end of the latter extend the nerve fibrils 

 which join to form the optic nerve which follows the contour of the 

 head to enter the brain laterally. Reddish-brown pigment fills the 

 retina, the iris and also a ridge surrounding the eyes. There are no cells 

 which function as pigment cells alone. 



The accessory eyes do not actually replace the lost mouth parts. 



The primary eyes are extremely small. They have no corneal 

 hypodermis, no visual rods, no iris. There is a lens below which are 

 a few retinal cells. The nerve fibrils leave the cells proximally and the 

 nerve joins that from the accessory eyes almost immediately. 



The principal steps in the development may be outlined according 

 to the several nymphal stages somewhat as follows. 



The earliest primordia of the eyes are to be seen in the second 

 nymphal period, when through a proliferation and elongation of the 

 hypodermis two groups of cells are formed, one on each side of the mid- 

 ventral line of the head and also behind each of the antennae on the 

 dorso-lateral surface. 



By the third stage the areas on the ventral surface have increased 

 sufficiently to meet and the cells of the original groups protrude further 

 entad. The visual rods then appear. They grow out from the distal 

 end of the cells, a darkly staining spot on the end in question being 

 the first indication of their Coming. At practically the same time 

 nerve fibrils appear at the proximal end of these cells. After this the 

 cells thus far concerned sink below the adjoining hypodermis. 



Thereupon, in the earlier part of the fourth stage, this hypodermis 

 undergoes a change and pushing in from all sides becomes superimposed 

 on the Visual rods and forms the corneal hypodermis and the iris. These 

 then secrete the lens. The depositing of the pigment keeps pace with 

 the development of the lens. 



Before closing I wish mention the fact that the subject was sug- 

 gested to me by Prof. J. H, Comstock at Cornill University where 

 the first part of the work was done. The development was studied 



