36 Animal Life and Intelligence. 



CHAPTER III. 



REPRODUCTION AND DEVELOPMENT. 



WE have now to turn to a fresh aspect of animal life, 

 that of reproduction ; and it will be well to connect this 

 process as closely as possible with the process of life in 

 general, of which it is a direct outcome. 



It will be remembered that, in the last chapter, it was 

 shown that the essential feature in the process of life is 

 the absorption by living protoplasm of oxygen on the one 

 hand and nutritive matter on the other hand, and the 

 kneading of these together, in subtle metabolism, into 

 unstable compounds, which we likened to explosives. This 

 is the first, or constructive, stage of the life-process. 

 Thereupon follows the second, or disruptive, stage. The un- 

 stable compounds break down into more stable products, 

 they explode, according to our analogy ; and accompanying 

 the explosions are manifestations of motor activity of heat, 

 sometimes of light and electrical phenomena. But in the 

 economy of nature the products of explosion are often 

 utilized, and in the division of labour among cells the 

 explosions of some of them are directed specially to the 

 production of substances which shall be of permanent or 

 temporary use for digestion, as in the products of the 

 salivary, gastric, and intestinal glands ; for support, as in 

 bone, cartilage, and skeletal tissue generally ; or as a 

 store of nutriment, in fat or yolk. The constructive pro- 

 ducts of protoplasmic activity seem for the most part to be 

 lodged in the spaces between the network of formative 

 protoplasm. The disruptive products those of them, that 

 is to say, which are of temporary or permanent value to 



