128 PROCEEDINGS OF THE ACADEMY OF [Feb.? 



ganglia. During the larval growth the eye increases greatly in size 

 and mitotic figures are abundant, the mitosis always d viding the 

 cells lengthwise, so that the one-layered condition is retained until 

 the close of the larval period. 



During the semipupa stage, after the larva is sealed up by the 

 workers of the hive but before it assumes the true pupa form, the one- 

 layered epithelium gives place to a condition in which all the cells do 

 not extend all the way from the outer surface to the basement mem- 

 brane. This is brought about by the lengthening of some cells, the 

 shortening of others and by the rearrangement of the cells in a manner 

 to be described later. By the time the head has attained the size and 

 shape of the adult, the cells have arranged themselves so that the 

 ommatidia are completely formed and no more mitoses occur. The 

 development of the ommatidia from now on consists of the differentia- 

 tion of the cell elements until they assume their adult form. The 

 development of the eye as a whole consists of a thickening of the organ 

 and the laying down of a chitinous lens over the surface. 



At the sides of the eye of the young pupa the appearance is as shown 

 in text fig. 2, and the cells which correspond to the cornea! pigment 

 cells around the ommatidia are quite numerous and shade off gradually 

 into the cells of the hypodermis over the rest of the head. As the eye 

 increases in thickness by the lengthening of the ommatidia there ap- 

 pears a dipping in of the cells of the border, so that there is an invagi- 

 nation all around the eye where the secreting surface of the hypodermis 

 is pulled down. This is shown by a thin sheet of chitin which runs 

 around the eye (seen in section, text fig. 1) in the late pupa and adult 

 eye. This chitin is similar to the chitin of the body proper, but not 

 like that over the eye. This imagination must not be confused with 

 such an invagination as is described by Patten for the formation of the 

 lens layer, for the ommatidia are here completely formed and the cor- 

 neal pigment cells have moved to their place at the proximal end of 

 the cone before the dipping of the cells here described takes place. 



In the formation of the optic ganglia, which takes place by the 

 invagination of cells of the hypodermis, there is formed a brain sheath 

 a sheath of cells covering the ganglia and still continuous with the 

 hypodermis at the edge of the eye. This layer of cells runs along 

 proximal to the basement membrane and very close to it in the pupa 

 stage. As the retinular ganglia take on their final shape these cells 

 are pushed away from the basement membrane, and are seen in the 

 adult eye as strands of cytoplasm woven in among the nerve fibres 

 between the basement membrane and the retinular ganglion. The 



