INHERITANCE 



323 



life. A few weeks of lying in the sunwarmed marsh suffice 

 for the hatching of the eggs of the musk turtle (fig. 182), 

 which receive no parental care. Three weeks of persistent 

 incubation are necessary to hatch the eggs of the common 

 fowl, and a still longer period of maternal care after hatch- 

 ing is needed to get the chicks well started in their careers. 



Fig. 183. Sandpiper (precocious) a few days old, swimming. 

 Photo by G. C. Embody. 



The young of altricial birds (fig. 184) are fewer, hatch in a 

 more helpless condition, require to have their food brought 

 to them and put in their mouths, and receive the care of both 

 parents for a long time. Months of pre-natal nur- 

 ture are required for the development of the young of all the 

 larger mammals, and after birth, other months of nursing, of 



