TJie Evidence from Intellectual Differences. 247 



or indirectly, the product of a fertilized egg or seed, 

 through which the laws of heredity and variation act, to 

 bind the separate individuals into a progressive whole. 

 The seeds and eggs with which w^e are most familiar are 

 highly complicated, and consist of the protoplasmic germ, 

 which is intimately united to a mass of food destined 

 to be converted into protoplasm during development. 



The germ wdth its food forms the yolk of such an egg 

 as that of the bird, and is surrounded by layers of albu- 

 men, which are also used as food, and by a complicated 

 series of investing membranes. It originates in a special 

 organ, the ovary, and is incapable of perfect develop- 

 ment until it has been fertilized by the male reproduc- 

 tive element. In its earliest stage of growth it is simj^ly 

 one of the cells or histological elements of the ovary, but 

 as it grows it soon becomes very much larger than an 

 ordinary cell, and its protoplasm becomes filled ^\\i\\ 

 food material, and the outer layers and walls are added 

 to it. In many animals the external envelopes are want- 

 ing, and the egg is simply a very large ovarian cell, filled 

 with food material, and cai3able of developing, under the 

 influence of the male element, into a new organism. In 

 still other animals the food-yolk is wanting, and the egg 

 is small, and does not differ from an ovarian cell; and in 

 still other animals the ovaries are lacking, and cells may 

 become specialized as ova in various parts of the body. 



The sel'ies is so complete that we may be certain that 

 we are comparing strictly homologous structures, and 

 we may therefore conclude that the egg is nothing but 

 one of the cells of the body, w^hich may, when acted 

 upon by the male element, develop into a new organism, 

 substantially like its parents, with some of the individ- 

 ual peculiarities of each of them, and also with new pe- 

 culiarities of its own. 



