COMPARATIVE MENTAL CAPACITIES. 449 



co-operation of numerous citizens, understanding each other. 

 Numerous observations have placed the astoundingly high 

 intellectual development of these little Articulated Animals 

 beyond all doubt. With this let us compare, as Darwin 

 has done, the intellectual capacity of many lower, and. 

 especially, of many parasitic, Insects. There, for example, 

 are the Scale Insects (Coccus} which, when mature, consist 

 of an entirely immovable shield-shaped body attached to 

 the leaves of plants. Their feet are atrophied. Their 

 mouths are embedded into the tissue of the plant, the 

 juices of which they suck. The whole mental activity of 

 this motionless female parasite consists in the enjoyment it 

 derives from sucking these juices and from sexual inter- 

 course with the unattached male. The same is true of the 

 maggot-like female of the Twisted-wings (Strepsiptera), 

 which spends its whole life, wingless and footless, as a 

 motionless parasite in the body of the wasp. There can be 

 no suspicion of any higher mental activity there. If these 

 brutish parasites are compared with the mentally active 

 and sensible ants, it will certainly be admitted, that the 

 psychical differences between the two are much greater 

 than those between the highest and lowest Mammals, 

 between Beaked Animals (Ornithostoma), Pouched Animals 

 (Marsupialia), and Armadillos on the one hand, and Dugs, 

 Apes, and Men on the other. And yet all those insects 

 belong, without question, to the single class of Arthropoda, 

 just as all these Mammals undoubtedly belong to the single 

 class of Vertebrates ; and just as every logical adherent of 

 the doctrine of evolution must assume a common parent- 

 form for all those Insects, so also he must necessarily assert 

 a common descent for all these Mammals. 



