190 WONDERS OF ORGANIC LIFE. 



that, as a rule, all predatory or ferocious 

 animals are solitary (of course, we mean in 

 pairs,) but by way of exception the wild dog 

 hunts in packs, and so does the jackal. The 

 rat, which is partly carnivorous and partly 

 frugivorous, is, to a certain extent, a social 

 animal. At the same time we would only call 

 those animals truly social which establish com- 

 munities, each individual contributing a portion 

 of labour pro bono publico. Colonies of bees, of 

 wasps, of termites, of weaver birds, of beavers, 

 etc., afford us examples of what we here term 

 social animals, for they labour in a common 

 cause. Wild cattle, deer, and antelopes, etc., are 

 gregarious ; they herd together without any 

 definite purpose, and yet form troops, each indi- 

 vidual of which is acknowledged as a member 

 of the community. Shoals of fishes are, in our 

 acceptation of the word, congregational. Guided 

 by instinctive impulse, they associate together 

 in millions, but they act not in concert as do 

 rooks or wild, fowl, but even devour each other ; 

 none in the advancing phalanx gives the signals 

 of danger to the succeeding hordes. Most of 

 our migratory birds are truly gregarious only 

 for a season ; bound together by a voice which 

 says it is time to collect and depart, they obey 

 the call, and wing their way in assembled 

 thousands. We may here adduce the lemming 

 of northern Europe, which occasionally, in 

 myriads, migrating from its native region, 

 devastates the cultivated country. But no tie 

 binds these animals to each other. They unite 



