Heredity. 



as an egg, and the microscope shows in this egg no traces 

 of the organs of the dog's body or of anything at all like 

 them. So far as our means of examination go the egg is 

 no more like a dog than the mass of iron is like a steam- 

 boat. It may be said, though, that the dog's egg is not 

 left to itself, but is fertilized and is carried inside the 

 body of the mother until the new animal is matured; 

 that it is there nourished and built up from substances 

 supplied through the body of a full-grown dog; that it 

 may be acted upon at this time by agencies which have 

 a direct tendency to build up out of it an organism like 

 the parent; that the egg does not actually contain a po- 

 tential dog, but simply supplies the proper material to 

 be acted upon by the surrounding conditions, and that 

 the structure of the new animal is due to these condi- 

 tions; that the embryo becomes a dog because it is 

 bathed by a dog's blood, nourished through a dog's body, 

 and is completely surrounded by influences which are 

 peculiar to dog nature. Those persons who are not 

 naturalists derive their knowledge of the animal world 

 chiefly from our common domestic animals, and to 

 such persons this explanation may seem probable; but 

 naturalists, with wider experience, know that animals 

 which carry their young inside their bodies are excep- 

 tions, and that the organization of the future animal 

 must exist potentially in the egg, since the conditions to 

 which it is exposed cannot possibly have any tendency to 

 produce from it a being which does not already exist, in 

 some form, within it. 



A bee is almost as wonderful as a dog; its anatomi- 

 cal structure is exquisitely delicate and complex, and 

 every one is acquainted with the wonderful work which 

 it accomplishes. At the time it is laid the egg which 

 is to become a worker-bee contains no visible trace of its 



