186 



PRINCIPLES OF ANIMAL BIOLOGY 



ovoviviparity, and the laying of fertilized eggs prevail among land 

 forms, where protection against evaporation of the eggs is necessary; and 

 the habit of laying eggs before fertilization is mostly found among the 

 aquatic species and the amphil^ious forms which lay their eggs in water. 

 Care of Fertilized Eggs. — Among oviparous species the methods of 

 caring for the fertilized eggs are almost endlessly varied in their details. 



FxG. 155. — Nest of the Australian brush turkey, consisting of Utter in which the eggs 

 are buried to be hatched by the heat of tlie decomposing vegetable debris. The nest is the 

 heap of debris in the lower half of the photograph. {Photograph by E. R. Sanborn, loaned 

 by the New York Zoological Society.) 



There are many animals which give no care whatever to the eggs. This 

 is particularly true of aquatic species which pour the eggs and sperma- 

 tozoa freely into the water to come together by chance. The starfishes 

 and sea urchins and many other marine animals exhibit this lack of 

 parental care. Other forms merely put the eggs in places where develop- 

 ment is facilitated. Thus toads and certain salamanders which live 

 on land in the adult stage lay the eggs in the water. Aquatic turtles 

 come to land to lay eggs in the warm sand which hastens their develop- 



