430 William Morton Wheeler 



cerned, apparently as an adaptation to ethological requirements, 

 although the primary sexual characters have remained unaffected. 

 If it be true that the rudiments of the secondary sexual char- 

 acters are set aside so early in the development of insects and re- 

 main uninfluenced by the internal secretions, w^e can understand 

 why these characters exhibit no modification in cases of surgical 

 castration and why the modifications induced by alimentary, 

 nutricial and parasitic castration bear the aspect of inhibitions 

 or retardations of growth. Normal imaginal development in 

 insects, as is well known, depends on the amount of food accumu- 

 lated during larval life and stored up in the fat-body. In insects 

 surgically castrated during their younger stages there is nothing 

 to hinder the accumulation of this reserve material, and all the 

 imaginal characters, including the secondary sexual characters, 

 are thereby enabled to develop normally and completely. But 

 in insects that have been underfed or are infested with parasites 

 the reserve materials are either prevented from accumulating or 

 are consumed, so that the imago may have great difficulty in de- 

 veloping its imaginal characters. It is not surprising that under 

 such conditions the secondary characters are more or less reduced 

 or aborted, as we see in the forceps of parasitized Forficula males, 

 the thoracic and cephalic horns of male Scarabaeidae, the mandi- 

 bles of male Lucanidae, the wings of female Lasii, and many of 

 the other cases cited above. There is simply not enough nutri- 

 ment to permit of the full growth of the characters under consid- 

 eration. Their modification, therefore, is readily explained in 

 insects as due to malnutrition and we are not compelled to invoke 

 the internal secretions, or hormones, which play such an impor- 

 tant and interesting role in the sexual physiology of vertebrates. 



