I I 2 ZOOLOGY. 



time. Among the carnivorous forms, as the cat and dog, the 

 young are more helpless. In the human species the period 

 of helplessness is longest and consequently the necessity of 

 parental care greatest. In general, the longer period of 

 parental protection accompanies the development of more com- 

 plex and highly organized instincts, and intelligence. The 

 lengthened period of dependence, while a burden to the parent 

 in one sense, is an advantage to it in the saving in number of 

 offspring, and serves to benefit the species, not merely by keep- 

 ing the offspring alive until they may reproduce, but in the 

 greater development of such parental instincts as gentleness, 

 self-sacrifice, and the like. In the human race it has given rise 

 to the home and family, which we regard as the real basis of 

 modern society; and social organization in turn has been a 

 most powerful factor in the progress of the human species. 

 Death and the length of life must also be considered as special 

 adaptations. This differs in different species very widely. 

 Life in general, where natural selection acts, will be the period 

 of youth, plus the period of fertility, plus the time necessary 

 to rear the latest offspring. For the species, the death of the 

 individual becomes an advantage at the completion of this 

 period, and this fact is sufficient to insure that death will 

 normally occur at this time. 



148. Practical Exercises. Add instances of parental care which have 

 fallen under your own observation, and give a statement of the facts in 

 the case. Compare the mammals with which you are acquainted in this 

 regard. Compare the condition of the young of the robin, the quail, the 

 blue-jay, the pigeon as to maturity at hatching. Do any animals of your 

 acquaintance reproduce more than once in a year? Why is one reproduc- 

 tive period per year a common adaptation. Compile statistics concerning 

 the longevity of various animals, and its relation to size, to reproductive 

 period, and to the time demanded to reach the adult stage. 



149. Colonies. In some of the lower groups of animals, 

 as the polyps and jelly-fishes, in which the reproduction by 

 fission or budding is prominent, the newly-formed individuals 

 remain for a longer or shorter time in association with the 

 parent, or with each other. These units which otherwise might 



