224 ELEMENTS OF SCIENCE 



walls of which are replete with small glands, as are those 

 of the stomach, which latter secrete gastric juice. 



The generative function is a special modification and 

 form of " growth," while growth is a sort of self-genera- 

 tion. This is specially perceptible when any part which 

 has been destroyed is reformed, as when a broken bone 

 is repaired. Then the two broken edges become 

 softened, and a substance is secreted between them 

 which is at first jelly-like, then gristle-like, and at last 

 bony. In generation, impregnation is effected by the 

 junction of the spermatozoon with the ovum, which is a 

 process essentially similar to that of the union of anthe- 

 rozoid and pollen tube, with the female cells of the fern 

 and of the bean plant. Immediately after impregnation 

 very curious changes ensue, which cannot here be de- 

 scribed, the reader being referred for their explanation to 

 treatises on embryology.* Here it must suffice to say 

 that the first germ of the future animal appears in the 

 shape of a minute rounded mass of protoplasm, which 

 divides and divides itself again and again till three layers 

 of cells are formed, whence, by degrees, all the varied 

 tissues and all the complex parts which constitute 

 the kitten are gradually but rapidly built up. The 

 building up of the kitten, as it exists at birth, goes on 

 nevertheless in a roundabout fashion, various structures 

 being for a time formed which resemble conditions that 

 are permanent in lower animals^ but which subsequently 

 disappear or become much modified. 



The functions of the cat's nervous system merit some 

 special consideration, since without its aid none of its 

 other bodily activities could be carried on. Its functions 

 also present the most extreme contrast yet met with to 



* And to my work on the cat, p. 317. 



