240 Heredity. 



it should be much more active in them than it is in the 

 females, and we certainly find that this is the case. I 

 believe that we may, in justice, conclude that, with 

 greater knowledge of the few cases where females give 

 evidence that they have this power to an exceptional de- 

 gree, the difficulty will disappear, for they are certainly 

 deviations from a general rule, and they must therefore 

 be regarded as special cases, to be studied by themselves. 

 It is interesting to notice that both parthenogenesis and 

 female race- modification are more frequent among the 

 Anthropods than in most other groups of animals, and 

 that parthenogenesis is known to occur in the Lepidop- 

 tera and in the social insects, two of the groups where 

 great modifications can be most clearly traced to a fe- 

 male origin. It is not improbable that the power of the 

 egg to develop without fertilization, and its power to 

 store up and transmit gemmules, maybe related in some 

 way, so that when the one power is acquired the other is 

 also. 



Every one is aware that we meet, in the most diverse 

 groups of animals, with structures and instincts which 

 are confined to the females; such as the brood -chambers 

 of Daphnia, the ovipositor of the ichneumon fly, the 

 sting of the honey bee, the marsupial pouch of the op- 

 possum, the nest-building and incubating instincts of 

 birds, or the nursing habit of female mammals. We 

 must bear in mind, however, that in many of these cases 

 a male origin for the successive variations is not out of 

 the question. The fact that the male Hippocampus and 

 not the female has an incubatory pouch, and that mam- 

 mae are present in most male mamm;ils, certainly shows 

 the possibility of a male origin for these structures, and as 

 many male birds either share in the work of nest-build- 

 ing and incubating or aid the female in this duty, there 



