REPRODUCTION 5 



the very essence of the process. Not unnaturally so, 

 because reproduction was at first only known in man and 

 the higher animals. But since the life cycle of the lower, 

 more primitive organisms has become known, and especially 

 since the advent of the science of comparative anatomy, 

 we have learnt to view the process of reproduction from a 

 different standpoint altogether. 



To understand the problem thoroughly we have to begin 

 our study with the lowest organisms, in order to see the 

 process in its simplest form, and then follow it up gradually 

 in its evolution from stage to stage, until it attains its 

 highest form in the mammals, and ultimately in man. 



For this purpose, it is necessary, first of all, to give 

 a short resume of the modern conception of the living 

 organism — that is, of body and cell. 



(a) Body and Cell. 



All living organisms, plant and animal, are composed of 

 cells. The cell which forms the unit of the living being 

 may be defined as the smallest particle of organic matter 

 capable of life. The body consists of a mass of such units 

 — cells various in shape and function, and arranged in a 

 definite manner. One could perhaps get an approximate 

 idea of it by comparing it to a building constructed of 

 bricks and stones of different sizes, colours, and materials. 



The contents of the living cell — the protoplasm, as it is 

 called — is semifluid in consistence, ana generally enclosed 

 in a limiting membrane, which forms the outer hardened 

 layer of the cell. Within the protoplasm can be distin- 

 guished a small round body, the nucleus of the cell, which 

 has a special structure, and is the most important part of 

 the cell, inasmuch as it directs and regulates all the vital 

 processes going on in the cell-body. These functions are 

 assimilation, growth, and reproduction. The cell draws its 

 nourishment from the surrounding medium, and works it 

 up for its own purpose, turns it into protoplasm — i.e., 



