Sauropsida: Class Aves 537 



the spinal cord and of the brain exclusive of the pallium is predomi- 

 nantly of the automatic, reflex, or instinctive type. In a simple reflex a 

 nervous impulse initiated in some sense-organ is transmitted into the 

 spinal cord or brain and there passes over directly into a motor nerve 

 which connects with some effector — a muscle which contracts or a 

 gland which secretes. It is automatic and invariable so long as its 

 particular "reflex arc" is not acted upon by some higher dominating 

 center. Instinctive behavior is merely a highly elaborated system of 

 very complicated reflexes seated in a nervous mechanism which is 

 inherited unaltered from generation to generation. 



In the behavior of birds there is much that bears the outward 

 semblance of intelligent action. The uncritical observer marvels at the 

 skill, wisdom, and foresight exhibited by the bird in building its nest. 

 But the bird does not learn how. When the time comes to build the first 

 nest, the bird does it, and quite well. The pattern of the nest and of the 

 mechanism for building it were somehow in the egg which produced 

 the bird. Critical study of the bird's activities makes it clear that they 

 conform to a pattern characteristic for the particular species of bird 

 and so rigid that there is only a very narrow margin of possible modi- 

 fiability. Showmen exhibit their trained dogs, seals, horses, and ele- 

 phants, but birds are too little amenable to training to make an interest- 

 ing show. They do, to a limited extent, remember, learn, and profit by 

 experience, but so does a teleost fish whose pallium is devoid of nervous 

 tissue. In these capacities birds are probably somewhat inferior to 

 reptiles. 



It is probably safe to say that birds exhibit the most complex and 

 highly differentiated instinctive behavior to be found in the animal 

 kingdom, unless it is equalled by that of some insects and spiders. In 

 the structure of the bird's brain is to be seen extraordinary develop- 

 ment of all regions which have to do with activity of the nearly or 

 quite automatic sort, the corpus striatum becoming especially promi- 

 nent as the seat of instinctive nervous mechanisms. The teleost fish, 

 entirely lacking pallial nervous tissue, still has a certain small capacity 

 for modifying behavior. It is probable that in all vertebrates the cor- 

 relation centers of the corpora striata and regions posterior to it allow 

 for a small measure of modifiability. In the case of the bird, the weakly 

 developed pallium seems to add little, if anything, to the modifiability 

 which presumably exists in the lower correlation centers. 



The 12 pairs of cranial nerves correspond closely in all particulars 

 with those of reptiles. 



Reproduction 



Reproduction in birds is essentially similar to that in reptiles. No 

 birds, however, are viviparous. The eggs, relative to size of body, are 



