82 HEREDITARY CHARACTERS 



however, these ants act in concert in the most remarkable 

 manner, the fierceness of the individual being subordinated 

 to the various necessary tactical movements, even when 

 these involve retreat. Their mandibles are so modified 

 from the usual form, that they are practically useless to the 

 owner except for fighting. The ant is thus not only unable 

 to perform the delicate actions involved in feeding its own 

 larvse, but it is quite unable to feed itself, and will starve in 

 the midst of plenty unless its slaves are there to feed it. 

 P. rufescens attacks the nests of other ants, killing many of 

 them, and carries off some of the larger pupaa. When these 

 hatch out, they serve their masters willingly and faithfully, 

 even fighting in defence of the nest. In an allied American 

 species, the slaves even carry their masters and mistresses 

 when the colony migrates, as the latter do nothing for 

 themselves. The extreme of dependence is exhibited by 

 Anergates, which is unable to feed itself or its larvae, and 

 would be quite unable to cope with the other ants that live 

 with and tend it did the latter decline to serve. How 

 Anergates obtains the slaves, and why they serve it, is at 

 present an unsolved problem. 



A common " winter moth," Hybernia leucophcearia, 

 which frequents the bark of oak-trees, has dark and light 

 horizontal lines upon its wings, matching the colours of 

 the oak-bark. When this moth settles upon the bark it 

 nearly always assumes a horizontal position, " thus bringing 

 the lines of the wings into parallelism with the dark shadows 

 in the vertical cracks of the oak-bark." In this position 

 the moth escapes the notice of its enemies. 1 A moment's 

 thought must show that this instinct is kept up because 

 those individuals that vary away from it run enormous risks 

 of being killed by insectivorous animals, and so only those 

 which have it in full have a good chance of producing 

 offspring. To these they transmit their own characters, 



1 Hamm, A. H., Trans. Entomological Society of London, pp. 321-23, 1885, 

 and pp. 483-85, January 1907. (In the latter paper several other similar 

 instances are described.) 



