ADAPTATION 357 



ries the eggs in its mouth until they hatch. The number of eggs 

 found in a single individual male varies from 2 to 55 in observed 

 cases. The eggs are held loosely in the mouth and are subjected 

 to effective aeration by the water streaming over them and out 

 through the gill clefts at either side of the mouth. So far as 

 known the male does not feed during the time the eggs and the 

 developing young are in its mouth, which may be 70 days. 



The actual time required for the development of mammals 

 to the adult state is considerably longer than for other animals. 

 In general, mammals that depend primarily upon speed for escape 

 from danger do not have helpless or unprotected young, and in 

 such cases either the young are able to move rapidly as soon as 

 born, or they are brought forth in some secluded spot. Thus, the 

 young of the ox or deer are capable of running or walking shortly 

 after birth. Of course, the young are dependent upon the 

 mother's milk for food — as is the case with all mammals — but 

 in times of danger they are capable of fleeing with the mother. In 

 the opossum and also in the kangaroo, the young are born in 

 an extremely immature condition but are at once transferred into 

 a large pouch formed by a fold of the skin of the abdomen in 

 which they are carried (Fig. 200). According to the observations 

 of Hartman, in the case of the opossum the newly born animal 

 reaches the pouch by its own efforts. In the pouch the young 

 grasps the nipple of the mammary gland, from which milk is 

 forced into the mouth by mammary muscles, strangulation being 

 prevented by the prolongation of the larynx into the naso- 

 pharynx. Even after the young kangaroo runs about, it often 

 retreats to the pouch. Rodents and carnivores also bear their 

 young in a relatively immature state of development. Newly 

 born rabbits or kittens are blind and remain so for days, during 

 which time they are dependent on the parent for both food and 

 protection. In each case the young are brought forth in a 

 secluded place. 



• A consideration of adaptations emphasizes the fact that living 

 demands an adjustment between the organism and its environ- 

 ment. Without its environment the organism does not exist. 

 It has been said that "evolution is no more than adaptation of 

 organisms to environment" (Osborn). The debate as to the 

 origin and method of development of adaptation is of minor 

 consideration in comparison with the importance of the fact of 



