INSECTS 253 



olfactory function. Whatever their function, there can be 

 little doubt that they are moved about actively when in use, 

 and thus the stimulation to their development has never 

 been wanting. The excessive development has doubtless 

 resulted from excessive use. If they are organs of touch, 

 they may possibly be used in finding the female in the 

 following way : the Noctuidae generally live on and near 

 the ground, and the males might fly about over the ground 

 or grass with their palpi extended and moving until these 

 organs came in contact with a female. 



Coleoptera. In the Longicornia or Cerambycidae the 

 antennae are usually much longer in the males. These organs 

 are doubtless employed either for touch or smell, or both, in 

 finding the females, and it is in accordance with the greater use 

 that is made of them that they should be enlarged in the males. 

 In a few species the sexes differ in colour, and although I have 

 no evidence on the point, it is probable that in these cases 

 the habits are different. In any case, it is stated that the 

 bright-coloured species expose themselves in the daytime on 

 flowers and plants, while the dull-coloured forms do not 

 leave their hiding-places until twilight. 



In the Lamellicorns occur sexual differences as marked as 

 in any instance in the animal kingdom. The unisexual 

 characters of the males are often horn-like projections from 

 the head and thorax, which in many species exhibit an 

 extraordinary development. Darwin, being unable to find 

 good evidence that these horns were used as fighting weapons, 

 came to the conclusion that they had been acquired as 

 ornaments. 



These excrescences are chiefly characteristic of the 

 Dynastides, a sub-family of the Scarabaeidae, among which 

 are found some of the largest insects know 7 n. The pro- 

 portional size of the horns is extraordinary. They project 

 from the dorsal surface of the head and prothorax in such a 



