148 PROCEEDINGS OF THE ACADEMY OF [Feb., 



with the corneal hypodermal cells of the crustacean and aptorygote 

 insect eyes. In all crustacean compound eyes small nuclei arc de- 

 scribed as lying distal to the cone cell nuclei (or Sempcr's nuclei), and 

 these are the nuclei of the cells which secrete the lens. When the 

 ommatidia are arranged in facets, two such cells are present. In the 

 Apterygota, e.g., Lepisma saccharinum, Orchesdla, etc. (Hesse, 1901), 

 these two cells are present and occupy a similar position or ma}'- be 

 placed slightly more laterally. These two cells are characteristic of 

 these two types of compound eyes. On the other hand, the compound 

 eyes of most pterygote insects have the two pigment cells of the first 

 order (corneal pigment cells), and do not have the corneal hypodermal 

 cells, Hesse (1901) concluded that these two kinds of cells are homolo- 

 gous from an examination of adult eyes, and considered his point 

 strengthened by the fact that Johansen had described these pigment 

 cells as being distal to the cone cells at an early stage. Johansen did 

 not describe them as homologous, however, and derived the lens from 

 another source. From an examination of Apis I am convinced that 

 Hesse was correct in his deductions, for in this case the cells are not 

 only homologous, but the pigment cells here have identically the same 

 function as have the corneal hypodermal cells of the other eyes. 



As mentioned above, Johansen failed to see this homology and de- 

 scribes and figures the lens as being secreted by the cone cells. It has 

 been pointed out with sufficient detail that no such interpretation is 

 tenable for Apis at least, and we may well doubt its occurrence in 

 Vanessa. In PI. 23, fig. 11, he figures the secretion of the lens by the 

 cone cells and shows the corneal pigment cells extending to the distal 

 margin, and I am led to conclude that he has overlooked the position 

 of the pigment cell which remains distal to the cone. 



d. The Outer Pigment Cells. — These cells from the earliest larva to 

 adult stages extend the entire length of the ommatidium, and are what 

 are known as accessory cells in many eyes. They, like all the other 

 cells of the eye, are of ectodermic origin, there being no cells from 

 the mesoderm in the eye of Apis, such as are described in some eyes. 

 These cells are, normaUy, twelve in number, but when hair cells are 

 present between the ommatidia, which is very frequently the case, this 

 number is increased so that any definite enumeration is impossible; 

 and since these cells serve merely to fill the interornmatidial spaces 

 and to prevent reflection inside the lens, no more definite arrangement 

 is required. The nuclei of these cells lie proximal to the cone in pupal 

 stages, but in the lengthening of the cone they come to lie at about its 

 middle. 



