Amerkmi Museum of Natural Uistory 



SEXUAL DIMORPHISM IN INSECTS 



The cabbage butterfly, the female having two spots on the front wing, in addition to 

 the dark tip 



in place, in the absorbing of excess food which is normally passed on to the 

 next generation. And there is almost uniformly a marked difference in size 

 between the male structures — or even individuals — and the female, the female 

 being generally the larger. Looked at from this point of view, maleness and 

 femaleness seem to extend to many traits of plants and animals that are not 

 directly connected with reproduction. 



Secondary Sexual Characters We may see that in both plants and 

 animals there are many characteristics which have nothing directly to do 

 either with getting food and growing or with splitting off special reproductive 

 cells — whether spores or gametes. In connection with producing and dis- 

 charging eggs and sperms, some of these supplementary structures and proc- 

 esses seem to get far away from the essentials. We speak of such organs and 

 activities as secondary sexual characters. The differentiations between male 

 and female individuals are most striking and elaborate in flying animals — 

 birds and insects. We can understand these as being in a way related to the 

 fact that the gametes have to be brought together in a fluid medium. But 



Aiiicrican Museum of Natural Uistory 



SEXUAL DIMORPHISM IN CRUSTACEANS 



Female and male of the fiddler crab, Uca brevifrons 



391 



