54 THE POPULAR SCIENCE MONTHLY. 



centipede as tbc representiitwe of a dawning instinct and its appropri- 

 ate manifesting organ, the sensorium, it was found that reflex action, 

 characteristic of acephalous animals, did not cease when the head and 

 its special ganglia appeared, but that a large share of its actions was 

 still purely reflex in character, even those prompted by its small and 

 imperfect sensorium being but little raised above the reflex and into 

 the region of instinctive actions ; and that the ganglionic system and 

 reflex action were continued all through the higher mollusks and the 

 whole series of articulates, only diminishing in importance as the sen- 

 sorium and instinctive action increased. So in the commencino- verte- 

 brate series, we find the nervous organization of the preceding races 

 continued that for reflex action being represented in the spinal cord, 

 and that for instinctive action being continued in the sensorium ; not 

 only so, but in proportion as the cerebrum remains small and imdevel- 

 oped, and the sensorium j^rcdominates, do instinctive actions remain 

 in the ascendant both in nimibcr and importance. This is found to 

 be true in all the lower orders of vertebrates fishes and reptiles ; and 

 even in the lower mammalians, although the cerebrum may outweigh 

 the other portions of the brain, still a very important part of the 

 actions manifested is instinctive. As an example of tl'iis in birds. 



Fig. 4.-BEAIX of Pigeon: 1. Cerebrum; 2. Optic Ganglia; 3. Cerebellum; 4. Optic Nerve ; 



5. Spinal Cord. 



may be mentioned the chick, which breaks its prison of shell with its 

 beak and immediately runs about, sees and picks up its particle of 

 food with unerring certainty without teaching or experience, hears 

 and answers the call of the mother-bird, and scrambles toward her for 

 protection although it may never have seen her. Birds also possess 

 in a remarkable degree the impulse, akin to that of insects, for pre- 

 paring elaborate habitations ; but unlike the insect races they add a 

 certain degree of intelligence to their work, varying it in form and 

 material according to locality and surroundings, and even finishing for 

 their own use that which others had left incomplete and abandoned. 

 In proportion as instinct ceases to predominate, the work becomes less 

 uniform ; and so it may be observed in general, that in proportion as 

 the habits of a given race are fixed and automatic, does each individ- 

 ual conform in its action to that prearranged method, and we know 

 what each individual under given circumstances will do ; but, as Intel- 



