296 THE HUMAN SPECIES 



party shares its food with the other, or finally to vital-com- 

 panionship, where the parasite either lives in the skin, or in the 

 viscera of its host. As a rule, the parasite is a lower species 

 than the host, but there are exceptions to this, for not only do 

 animals of the same rank act as host and parasite (namely, insects 

 on insects, or crabs on crabs), but sometimes actually a higher 

 animal lives on a lower (crabs on molluscs and fish on echi- 

 noderms). The most remarkable instances are however those 

 of the male, the smaller sex of the species, living a parasitic 

 life in the larger female, as sometimes occurs among the 

 bonellia, and certain crustaceans (wood lice and centipedes). 



Man does not make a very notable exception to this custom, 

 for have we not always with us the professional beggar, the 

 gipsy, and other tramps, the usurer, the thief and burglar 

 who without troubling to work for a living exist at the expense 

 of the community? If we turn, however, from parasitism 

 this dark side of the social instinct to the better aspect of the 

 mutual affection, we find that the expression of this impulse by 

 the individual which we call friendship is only found among 

 the higher animals (birds and mammals). 



Examples of friendship amongst birds, between birds and 

 animals, and between different species of animals, are well 

 enough known to make it unnecessary to quote them here. 

 It is a fallacy, however, to suppose that a friendship between a 

 dog and cat is quite impossible ; if the pair have been brought 

 up together the friendship between the two may subsequently 

 become even more firmly cemented than many human friend- 

 ships. 



The highest phases of individual affection are reached among 

 animals. Wundt 1 is of the opinion that these exist only 

 among the higher Vertebrates (birds and mammals), and not 

 among Invertebrates, or the lower Vertebrates. He does not 

 seem to be aware that among the chafers of which the well- 

 known Ateuchus sacer may be taken as the type, the males and 

 females care for their progeny so much that they form for each 

 egg a dung-ball ; fi'nally when the number is complete they 

 may end their life. Close investigation reveals, moreover, 

 among the lower Vertebrates a pairing between the male and 



1 Wundt, loc. cit., pp. 411-22. 



