40 Cunningham, Unisexual Inheritance. 



that investigators previous to Giard's discovery had stated that 

 only the females were attacked by the parasite, the truth being that 

 the males infested were mistaken for females. The secondary sexual 

 characters in the prawns are less marked than in crabs, they consist 

 in modifications of the first two pairs of abdominal appendages for 

 copulatory purposes, greater length of the thoracic chelae, and greater 

 size of the olfactory branch of the first antennae. 



It might perhaps be argued that the effect on the primary gene- 

 rative organs, ovaries or testes, being due to the disturbed nutrition 

 of the host, the reduction of the secondary sexual characters was 

 likewise simply due to diminished nutrition: the supply of nourish- 

 ment being reduced the organs could not grow to their normal size. 

 But it must be remembered that reduction in the supply of nourishment 

 ought merely to reduce the size of the whole body, as starvation of 

 a young animal is known to do, it does not necessarily reduce parti- 

 cular organs in comparison with others. The correct interpretation 

 seems to be that the primary organs are not destroyed, but for want 

 of nourishment are unable to produce generative products, and it is 

 this functional development which is correlated with the development 

 of the secondary characters. 



The case of Stylopised bees to which Professor Me Idol a refers 

 is precisely analogous with the cases of parasitic castration in Crustacea 

 to which I have already referred. The facts in this case were care- 

 fully and successfully investigated by Professor Perez of Bordeaux 

 in 1879. It was originally supposed that the bees carrying the para- 

 site formed distinct species, but Perez found that they were indi- 

 viduals of other species modified by the effects of the parasite. The 

 parasite Stylops is believed to belong to, or to be allied to, the 

 Coleoptera or beetles. The minute active larva soon after it is hat- 

 ched obtains entrance into the body of a larva of a solitary bee of 

 the genus Andraena, and there changes into a footless maggot which 

 lives at the expense of its host without killing it. The female stylo- 

 pised Andraena has a head somewhat smaller than normal, the ab- 

 domen more globular, and more hairy : the most remarkable peculiarity 

 is, however, that in the female the posterior legs are more slender, 

 and their pollen brushes either much reduced or absent. The ovi- 

 positor is also reduced. The modifications of the male are of less 

 degree, consisting chiefly in the loss of the coloration proper to the 

 face. M. Perez found that in the female the development of the 

 ovaries was completely arrested, and mature eggs were never produced, 

 while in the male only the testicle of the side on which the parasite 

 lies was affected, the other producing normal spermatozoa. In this 

 case it is evident that the modifications of the hinder legs in the fe- 

 male bee are secondary sexual characters. It must be remembered 



