1905.] NATURAL SCIENCES OF PHILADELPHIA. 147 



become crescent-shaped, and finally almost encircle the apex of the 

 cone. Strands of cytoplasm connect the nucleated portion of the cell 

 with the distal portion, which remains at the point where secretion is 

 to take place. As the cone enlarges and the cell substance of the cor- 

 neal pigment cells is used up in the secretion of the lens, the portion 

 distal to the cone becomes reduced until in the adult eye it is almost 

 entirely absent. 



Almost immediately after pigment is first formed in the retinula cells, 

 it begins to be deposited in these corneal pigment cells. Owing to the 

 fact that the retinula pigment is at first small in quantity, and since 

 there is none in the outer pigment cells at this time, the pigment of 

 these distal pigmented cells, which is red, gives a pink color to the en- 

 tire eye in the early stages, rather than the brown or black color pos- 

 sessed by the other pigment, as is true in late stages. 



The granules of pigment are large and red in color, and when treated 

 with depigmenting mixtures do not disappear, but become somewhat 

 lighter in color. 



The lens is secreted by these cells in much the same way as is ordinary 

 chitin over the entire body of the bee. This chitinous covering is 

 deposited in layers which are easily visible in the adult lens. In 

 addition to these cells the outer pigment cells also seem to enter into 

 this. In the pupal eyes before any chitin is deposited by the corneal 

 pigment cells thin sheets of chitin extend out from the outer pigment 

 cells, and since these cells arc arranged at their distal ends in a nearly 

 hexagonal manner a cross-section of these plates shows the future 

 boundaries of the facets. In the adult eye the portion of the cornea 

 which directly overlies the outer pigment ceUs differs slightly from the 

 part directly over the cone in refractive index and in general appear- 

 ance, so that I think it probable that the space between these sheets of 

 chitin in the larva is filled by a secretion of the outer pigment cells. 

 If this be true, then every cell which enters into the formation of the 

 compound eye has to do with some sort of secretion, either intra- or 

 extracellular. 



The structure of the chitin laid down by the corneal pigment cells is 

 not uniform, the outermost layer being more dense than the rest, with 

 a decided tendency to take up an iron haematoxylin stain, the middle 

 or main portion being arranged in alternating layers of different den- 

 sit3% and the inner portion taking a protoplasmic stain, such as eosine 

 or Bordeaux red. 



From this description it will be seen that the corneal pigment cells 

 (Hauptpigmentzellen, pigment cells of the first order) are homologous 



