1905.] NATURAL SCIENCES OF PHILADELPHIA. 139 



them, since it scarcely seems probable that both plans exist, since all 

 ommatidia are probably the result of one kind of development. 



Patten bases his view on the fact that the cone cells are continuo\is 

 with and part of the rhabdome, but surely in Apis there is no such 

 continuity, since all through the development they are separate, and in 

 the adult eye there is a sharp line of demarcation between them, and 

 they also react very differently to stains. In Vespa, Patten admits 

 that the rhabdome is not continuous with the crystalline cone cells, but 

 in this case he describes processes between the rhabdome and retinula 

 which correspond to the processes which form the rhabdome in other 

 forms. Since, as will be discussed later, the rhabdome is really part 

 of the retinula, being formed as an intracellular secretion, any such 

 process from the cone cells would have to pierce the retinula cells to 

 occupy such a position. No such processes occur in Apis. If such a 

 view be held because it is necessary in some way for the nerve fibres to 

 reach the crystalline cone, on the assumption that the nerves end there, 

 such a necessity disappears, for, as will be shown under a discussion 

 of the innervation of the ommatidium, the cone is in no way a nerve 

 terminus. Such a theory of innervation does not seem justified for 

 any ommatidium, and therefore the necessity for this conception of 

 the morphology disappears. 



On the other hand Watase based his view largely on the eye of 

 Limulus. This view commends itself on account of its extreme sim- 

 plicity, since all ommatidia readily lend themselves to the plan of 

 diagrammatic representation used by Watase with this interpretation. 

 Watase seems to have advanced this theory rather for the purpose of 

 giving some explanation for the existence of the rhabdome than for 

 the morphology of the entire ommatidium. There is, I think, no reason 

 to believe that the rhabdome was ever a chitinous substance, and in 

 that sense it is not homologous with the lens. In the ommatidium, 

 as we now know it, the rhabdome is an intracellular secretion full of 

 nerve fibrils, and is far from being a hard chitinous growth. To that 

 extent, then, Watase's conception seems an error. If, however, we 

 look on the lens, cone substance and rhabdome as secretions (non- 

 living protoplasmic differentiations), of which the lens only is an extra- 

 cellular secretion, then the homology may hold. Acording to this 

 view, then, the ommatidium did not arise as a pit filled with chitin, 

 but rather the sinking in of certain cells, with a corresponding retention 

 of the secretion inside the cell, has taken place with the assumption of 

 new functions. Parker has argued that the retinular cells cannot be 

 considered as homologous with the lens secreting cells, since the lens 



