THE GROWTH OF GROUPS 125 



been observed as the offspring of multitceniata, and both 

 have been found in groups. In regard to melanothorax, 

 Tower says, " I have reared this form from eggs laid by 

 multitceniata. It is an elementary species which appears 

 at various localities at frequent intervals, but which has 

 not yet been able to become established as a member of 

 the fauna of the habitat into which it is born." 



The question when is a species a member of the 

 fauna of the habitat into which it is born, and when is 

 it not a member ? seems to be unanswerable, since there 

 is no fixed convention to appeal to. We can describe 

 animals as we see them and inquire how they came to be 

 in that state. What more can we do ? However, even 

 if we do not take this view, if we know what a species is, 

 and are sure that small groups exemplified by the melano- 

 thorax beetles or by the white-bellied rats, appearing 

 temporarily here and there, are not really species ; yet 

 we cannot deny that such small groups occur. It has 

 been the custom to regard sports as negligible, must we 

 also regard small groups of them as negligible ? 



The form rubicunda is perhaps a species in the usual 

 sense. In the year 1903 it was found over an area of 

 seven or eight square miles at Toluca in Mexico, three 

 years later the area of its distribution was found to be 

 about ten acres, hence the species is waning or may even 

 now be extinct, but in 1903 it was a large group. 



A number of multitceniata, collected at Guadeloupe in 

 Mexico, were taken to Chicago and allowed to breed in 

 captivity under conditions which were nearly normal. 

 The great majority of the offspring raised were of the 

 kind multitceniata, like their parents, but both rubicunda 

 and melanothorax were born in the same line as sports. 



