I20 



ZOOLOGY 



some insects, especially the social forms, such as bees, ants, and 

 the like. The lobster carries its young on its abdominal ap- 

 pendages for months after hatching. The lower invertebrates 

 are practically destitute of these later care-taking instincts. 



It is interesting to notice that animals differ very much in 

 their helplessness at hatching or at birth. The young of the 

 reptiles, or the duck, or the chicken are relatively well developed 



Fig. 56 



Fig. 56. Nestling Marsh Hawks (Circus cyaneus hudwnius). From Year-Book. Department of 



Agriculture. 



Questions on the figure. — What are the nesting and breeding habits of the 

 marsh hawk? Are the young precocial or altricial? 



at hatching, and are very soon able to run about and feed {pre- 

 cocial). The young of the song birds, as the thrushes, swallows, 

 etc., are wholly dependent on the care of the parents for a con- 

 siderable time {altricial). In the herbivorous mammals, as the 

 sheep and cattle, the young have the use of their limbs in a short 

 time after birth. 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 



