I9IS.] PARKER— THE PROBLEM OF ADAPTATION. 5 



males, the drones, are set off against one perfect female, the queen, 

 and a host of imperfect ones, the workers. These cases differ from 

 those in the higher animals, however, in that the sex ratios appro- 

 priate for the breeding colony are determined from the beginning, 

 i. e., the young are not produced males and females in equal num- 

 bers. Such cases as the honey bee and other like insects exhibit, 

 therefore, in their sex ratios much more accurate adjustments to 

 their breeding requirements than do the higher animals ; in fact they 

 may be said to show a very high order of intracolonial sex adap- 

 tation. 



Throughout the animal kingdom as a whole sexual reproduction 

 seems to be best adjusted where the sexes are represented in ap- 

 proximately equal numbers and this relation is probably determined 

 by the production of equal numbers of male-determining and female- 

 determining sexual elements. The sperm cells of most species of 

 animals, perhaps of all, are apparently the prime factors in this de- 

 termination, and the dimorphism of these cells in the sense that one 

 class is made up of male-determiners and the other of female-de- 

 terminers as well as the production of these two classes in equal 

 numbers may be looked upon as the chief adaptation of the animal 

 kingdom so far as sex ratios are concerned. But the reproductive 

 activities of a limited number of animals, such as the honey bee and 

 the fur seal, have developed in directions in which equal numbers 

 of the two sexes serve no longer as an advantageous combination. 

 To meet these new conditions, further adaptation would be needed 

 and, from what has been said, this adaptation would involve read- 

 justments in the powers of the sex-determining reproductive cells. 

 Such readjustments seem to have been carried out in the insects as 

 seen in the honey bee, etc., where through the development of nat- 

 ural parthenogenesis the usual sex ratio has been entirely set aside 

 and a new one favorable to the new requirements has been estab- 

 lished. This has not been accomplished by the fur seals and other 

 higher animals which in this respect remain poorly adapted to their 

 new relations. From this standpoint, then, such lower animals as the 

 insects show a higher order of adaptation than either the mammals 

 or the birds. An explanation of this paradox may be found in 

 the fact that the rate at which generation follows generation in in- 



