CHAPTER I. 



DESCRIPTION OF THE SEXUAL PRODUCTS. 

 EGG-CELL AND SEMEN-CELL. 



IN most animals, and without exception in all Vertebrates, the 

 development of a new being can take place only when reproductive 

 elements, produced by two sexually different individuals, the egg 

 by the female, and the seminal corpuscle or seminal filament by the 

 male, are at the proper time brought into union as the result of 

 the procreative act. 



The egg and the seminal filament are simple elementary parts or cells, 

 which are produced in special glandular organs, the egg-cells in the 

 ovary of the female, and the semen-cells in the testis of the male. 

 After the beginning of sexual maturity at definite periods, they 

 detach themselves within the sexual organs from their union with 

 the remaining cells of the body, and form, under suitable conditions 

 of development, among which the union of the two sexual cells is 

 the most important, the starting-point for a new organism. 



First of all, therefore, we have to acquaint ourselves with the 

 peculiarities of the two kinds of sexual products. 



1. The Egg-cell. 



The egg is by far the largest cell of the animal body. At a time 

 when nothing was known of its cell-nature, its separate components 

 were given special names, which remain in use even at the present 

 time. The contents were called egg-yolk, or vitellus ; the cell- nucleus 

 was called vesicula germinativa, or germinative vesicle, discovered by 

 the physiologist PURKINJE ; the nucleai corpuscles, or nucleoli, were 

 called germinative spots, or maculce germinativa} (WAGNER) ; and, 

 finally, the cell-membrane vas called the yolk-membrane, or mem- 

 Itrana vitellina. All these parts vary in not unimportant ways from 



