CAUSE OF HEREDITY 293 



thesis not only fails to explain this, but a careful consid- 

 eration of its postulates shows that the co-adaptation of 

 living organisms to each other and to their environment 

 and the origin of species by mutation are incompatible. 

 There is no living organism which would not serve as an 

 example of the phenomenon of adaptation. We must, 

 however, consider a few individual cases in order to real- 

 ize its full significance. 



"Sitaris humeralis, a beetle belonging to the family 

 cantharidae is a parasite upon the solitary bee, antho- 

 phora. The female Sitaris lays over 2,000 eggs, burying 

 them in the earth near the entrance to the nests of the bee. 

 These eggs hatch, producing larvae, which possess six 

 legs, as is usual in the larvae of beetles. The larvae are 

 triungulins, that is, they possess three claws at the ex- 

 tremity of each leg. This is exceptional among beetle 

 larvae. The larvae hibernate until the following spring 

 when they become active. They do not, however, try to 

 enter the nests of the bees, but attach themselves to any 

 hairy object that happens to approach them. No discrim- 

 ination is shown in the choice of an object beyond the 

 fact that it must be hairy. The majority of the larvae are 

 doomed to extermination for they attach themselves to 

 any hairy object with which they come in contact and 

 there is a vastly greater number of chances that they will 

 fix upon the wrong than upon the right insect. The} 

 have been found upon hairy beetles, flies and bees of the 

 wrong kind. Those, however, which are fortunate enough 

 to chance upon Anthophora are carried to the nest. Now 

 the male Anthophora appears about a month earlier than 

 the female, therefore, most Sitaris that arrive at their 

 proper destination are attached to the males. They trans- 

 fer themselves, however, to the female. When the female 

 Anthophora lays her eggs in the cells of the nest the 



