138 PROCEEDINGS OF THE ACADEMY OF [Feb., 



youngest pupal eye observed (just after the semipupa stage). The 

 number of nuclei around the spindle throws no light on this, since they 

 are still dividing occasionally and their number in the adult is not 

 fixed. 



Considerable stress has been laid on the fate of this spindle-shaped 

 mass of cells, since the determination of this fact alone is of such great 

 importance in the consideration of the morphology of the ommatidium. 

 That the outer pigment cells are morphologically peripheral to the 

 crystalline cone and retinula no one would deny. The position of the 

 corneal pigment cells might be a doubtful point if they were derived 

 from a separate layer of cells formed by invagination of the entire eye, 

 but as no such invagination occurs in the bee, and as at an early pupa 

 stage they are clearh^ outside the cone, I think there can be no doubt 

 as to their morphological position. The question as to the relative 

 morphological position of the crystalline cone cells and the retinular 

 cells is, however, not so clear. 



According to Grenacher the ommatidium is two-layered, and the 

 lens and cone are morphologically distinct from the retina. If this 

 view is held, then the question stated above does not exist; but such 

 an interpretation can no longer be held on comparative anatomical 

 or embryological grounds, as has been shown so well by numerous in- 

 vestigators, the evidence for which it is not necessary to give here. 

 Suffice it to say that, as has been shown previously, the ommatidium of 

 Apis arises from a one-layered epithelium, and all the cells are morpho- 

 logically equivalent. Taking into consideration, then, only such views 

 as are based on such interpretations, we find two opposing theories. 



According to Patten, Kingsley and others, the crystalline cone is 

 sometimes continuous with the rhabdome; these two would therefore 

 be the morphological centre of the ommatidium, while the retinula 

 must arise from colls outside this. When the crystalline cone is not 

 continuous with the rhabdome. Patten still considers the cone as the 

 centre, since he describes processes running from each cone cell around 

 the rhabdome but inside the retinula (as in Vespa). To this interpre- 

 tation those investigators who consider the crystalline cone as the 

 terminus of the nerve fibres would probably agree. On the other 

 hand, Watase holds that the ommatidium is a morphological invagina- 

 tion of which the retinula is the centre, and the cone cells, lens cells 

 (homologous with the corneal pigment cells of Apis) and pigment cells 

 follow in the order named. By this interpretation the rhabdome, cone 

 substance and lens are homodynamous. These two views seem in no 

 way reconcilable, and more investigation is necessary to decide between 



