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THE NA TU RE-STUD V RE VIE W 



|3 :5— MAY, 1907 



the part played by the two species, respectively. At first 

 glance the black slaves may be distinguished from their somewhat 

 larger red masters. Here and there the former may be observed 

 digging tunnels, "milking" the so-called ''ant-cows" or aphids 

 and then feeding the young, cleaning the nests, and in many 

 other ways performing the many domestic duties of the colony. 

 Rarely, if ever, do these duties take them outside the nest and then 

 only in their quest for new aphids. This important activity seems 

 to be entirely in their charge. On the other hand, the masters far 



Fig. 2 —a, The slave-maker Polyergus and b, a mandible of the same, c, the Formica 

 slave and d, a mandible. 



from lying about unoccupied, as might be supposed, take an 

 active part in their own affairs. They seem to be most interested 

 in those activities which relate the colony to the outside world. 

 Thus they determine the migrations, at which times they may be 

 seen carrying their precious slaves from place to place ; and they 

 fight their battles and obtain their own food, all of which is no 

 small task when the size of many of these mixed colonies is con- 

 sidered. 



Not all the colonies of this species are slave-makers. This is 

 especially true of the American sanguinaries, among which, as 

 Wheeler has shown, the largest colonies are very often pure. 

 This would indicate that as the colonies become more and 

 more firmly established they refrain from the further pillage of 



