58 THE PLAY OF ANIMALS. 



some species the female workers have the slaveholding 

 instinct. This instinct must have arisen hefore the spe- 

 cies had sterile workers (they have developed from fe- 

 males originally productive); for all the intermediate 

 stages are known between those which hold no slaves at 

 all and those which always do it. The Formica san- 

 guinea do not yet show the slaveholding tendency as a 

 fixed and demonstrable characteristic of their species, nor 

 have they the extraordinary physical modification that 

 marks the Pohjergus refescens, settled slaveholders. Ac- 

 cordingly, we have here two developmental stages with 

 clearly marked instincts. It is between these two stages 

 that the variation to sterile workers must have taken 

 place. The jaws must be changed from working tools to 

 deadly weapons, as well as become adapted for carrying; 

 they have become sword-sharp pincers, sharp and strong, 

 suited alike for seizing and bringing home the young 

 from other nests and for boring into the heads of ene- 

 mies. At the same time the instinct for plundering is 

 enormously strengthened. And here the hereditary effect 

 of practice can not possibly be argued. The sterile 

 workers could not possibly transmit anything, and their 

 progenitors possessed neither such organs nor such in- 

 stincts. On the other hand, the domestic instincts are 

 weakened; workers of the Polyergus neither care for the 

 larv^ nor collect food and building material. In fact, 

 they seem to have lost entirely even the capacity to 

 recognise and appropriate their own proper nourishment. 

 " Forel, Lubbock, and Wasman are all convinced that 

 the assertion made by Huber long ago is entirely correct. 

 I have repeated his experiment, as well as Forel's, with 

 the same result. These insects starve when confined, if 

 none of their slaves are at hand to feed them. They 

 do not recognise a drop of honey as something that will 



