44 E VOL UTJON AND DISEASE, 



by no means harmless, for occasionally it enlarges and 

 becomes occupied by tumours, sometimes of large size 

 and complex constitution, which cause death from 

 mechanical interference with the brain. 



Darwin has pointed out that rudimentary (vestigial) 

 parts are apt to be highly variable. This variability 

 he thought was largely due to uselessness, and there - 



FIG. 22. A magnified view of a section through the pineal 

 eye of Hatteria. (After Baldwin Spencer.) 



fore to natural selection having no power to check 

 deviations in the structure of such parts. 



It will be interesting to study this view of the matter 

 in connection with oviducts, which are of frequent occur- 

 rence as anomalies in the males of unisexual animals, 

 especially as two reasons can be advanced for their 

 vagarious conduct. In the first place, I shall endea- 

 vour to show that they have undergone a remarkable 



