PARACOROTOCA AKEiniANI (WARREN). 343 



to the bi'aiii. In bleached sections it is seen that the cellular 

 elements of the onimatidia are quite abnormal (PI. XIX, fig. 52). 

 There are perhaps remnants of cone-cells (r. cL), but the 

 rhabdome cells bear no distinct rods, and they themselves 

 seem to carry the superabundance of pigment {p. c). Above 

 the optic plate we find large irregular spaces. 



The degenerate nature of the eye is perhaps an inherited 

 character which has been gradually evolved either through 

 the direct effect of the dai-kness of the termite nest on 

 numerous generations, or by the effect of the disuse of the 

 organ. If it were possible to rear an individual in full light 

 the eye might still be degenerate. From the condition of the 

 eye in the imago beetle it may be judged that, just as in 

 the blind fish Amblyopsis,i the later stages in the differen- 

 tiation of the retina are cut out of the ontogeny. The final 

 condition of the eye may be regarded as a partial histolysis 

 of a somewhat early developmental stage, and this is accom- 

 panied by a tendency to cut off the eye altogether from 

 the body by the development of an ingrowing shelf of 

 cliitin. 



The loss of eyesight must be to some extent disadvan- 

 tageous to the insect, especially since for the dispersal of the 

 species wandering from the parent nest must sometimes 

 occur. We cannot, therefore, regard the degeneration as 

 arising thi'ough the action of natural selection, but rather as 

 the inherited ill-effect of darkness or disuse. The tendency 

 for the cutting off of the degenerated eye by ingrowing 

 hypodermis secreting cuticle is to be looked upon as a 

 modification of the general tendency of the ectoderm to close 

 up a wound or to pinch off from the body a useless foreign 

 structure. 



Olfactory Organs. — Well-developed olfactory pits are 

 present. There is a ring of such round the terminal joint of 

 the antenna, and an especially large oval pit occurs in the 

 end-joint of the palp of maxilla 1. In some sense-organs 



1 Eigenmann, C. H., " The History of the Eye of the Blind Fish 

 Amblyopsis," ' Cont. Zoo. Lab. Indiana Univ.,' No. 50, 1903. 



