134 PROCEEDINGS OF THE ACADEMY OF [Feb., 



Vespa very similar to those here described, but I am unable to find 

 the nerve connections which he describes. Semper and Breitenbach 

 also describe such hair cells for Lepidoptera. 



The number of facets in the different kinds of individuals of the col- 

 ony differs considerably. The drones (males) have an extremely 

 large number of ommatidia, the eyes meeting on the top of the head, 

 and as a result the three ocelli are crowded down to the front of the 

 head. The workers and queens have a considerably smaller number, 

 about one-third as many, and the ocelli are located at the top of the 

 head. It is not clear why the drones should have a larger number of 

 ommatidia than the females of the colony, since they do not seem to 

 need so much larger range of vision. The only reason which might 

 be'suggested from a knowledge of the habits of the two sexes is that 

 at the time when the queen takes her "mating flight" she flies almost 

 directly upward, after a preliminary circle or two near the hive, and 

 then often flies to some distance from the hive ; this manner of flying 

 making more probable a mating with a drone from some other colony 

 than' her" own. Drones do not, as a rule, fly as high as does the queen, 

 and it would be advantageous to have the eyes extending to the top 

 of the head in order to follow the queen's flight. As soon as a queen 

 starts upward any drones which are flying near at hand start upward 

 after her, the eyes on the top of the head making it possible for them 

 to see her. 



To say that this difference has arisen on this account scarcely seems 

 justifiable, for it would seem easier for natural selection, sexual selec- 

 tion, or whatever other factor is potent here, to modify the habits of 

 flight rather than to enlarge an organ so much as in this case. This 

 much may, however, be said with a good deal of surety: two things 

 which would be likely to be acted on by selection in the bee are acute- 

 ness and range of vision and the power of flight. 



V. RETINULAR GANGLION. 



In the early larval stages the optic ganglia are clearly marked out, 

 but the retinular ganglia are not. The only indication of the retinular 

 ganglia is a number of cells which lie near the basement membrane of 

 the eye, principally at the posterior margin. During the larval growth 

 the nerve fibres from the ommatidia grow in from the retinular cells, 

 and as this growth goes on the cells of what are to be the retinular 

 ganglia are pushed farther away from the basement membrane and 

 assume their more definite position. Finally, in the adult animal the 



