252 SEXUAL DIMORPHISM 



of leaving progeny. But, as I have repeatedly urged, the 

 point is, Why is the inheritance limited to one sex ? and this is 

 explained on the theory that the elaborations of structure are 

 due to stimulations only affecting one sex. 



The olfactory sense plays an important part in guiding 

 the male to the female, and this sense resides in the antennas. 

 These organs are frequently specialised in the males, often to 

 an extreme degree in the Bombyces, especially in the Psy- 

 chida3, in which the female is often sedentary. In this case 

 the exercise of the sense and of the organ has evidently been at 

 work throughout the evolution. It is not merely the exercise 

 of the nerves of perception, which must be more stimulated 

 as the search for the female falls more exclusively on the 

 male, but the tissue of the antenna itself is doubtless exercised 

 by various movements and contractions produced by the 

 active efforts of the male to discover the required scent. The 

 acuteness of this sense in certain species is well known. Sir 

 Roland Trimen l states that the male of Lasiocampa Quercus 

 is attracted by the empty box from which a female has been 

 removed. 



In the genus Mastigoplioms, belonging to the Noctuidas, 

 and occurring in India and tropical America, there is an 

 extraordinary development of the mandibular palpi in the 

 males. These are elongated and bent so as to be carried 

 over the back ; they are not only much thicker and longer 

 than the antennas, but actually longer than the body. In the 

 females they are very much smaller. In the males they 

 terminate in fringes or brushes of long hairs. Unfortunately, 

 the function of these organs is not known. The palpi in 

 general are probably organs of touch, but possibly these 

 specialised palpi possess other senses. The fact that the 

 antennas are not specially developed in most of the Noctuidse 

 suggests that these enlarged palpi have taken over the 



1 South African Butterflies, p. 13. 



