240 THE CAT. [CHAP. vm. 



eight nipples four on each side, one close to the anterior, and one 

 near the hinder end of the glandular structure. 



These glands become greatly enlarged when in use, especially the 

 abdominal portion (Fig. 114). In the male the mammary gland is 

 quite rudimentary, though essentially similar in structure to that of 

 the female. 



These milk glands may be regarded as greatly enlarged and aggre- 

 gated sebaceous glands, and the milk which they secrete, as a modified 

 sebaceous secretion. The MILK they form is an opaque white fluid, 

 containing much water, with certain salts of potassium and sodium, 

 with phosphoric acid, iron, milk-sugar, some albuminous matters 

 (casein and a little albumen), with fats and some other substances. 



The milk being the destined food of the kitten, contains all the 

 materials needed for the nourishment and growth of the young 

 animal. It contains in fact a suitable and nicely balanced supply 

 of nitrogenous and non-nitrogenous, albuminoid, fatty, amylaceous 

 and saccharine matters. 



19. In the structures last described we have found organs 

 destined for the nourishment of another individual ; but we have 

 next to consider organs destined for the actual formation of other 

 individuals. Such are the organs of REPRODUCTION, or generative 

 organs : the business of which is to manufacture, and to render 

 serviceable certain diverse products which concur in giving rise to 

 a new living organism, destined with growth to become an animal 

 like that by which one or other of such products have been secreted. 



The products thus formed are essentially of two kinds, and the 

 faculty of forming one or the other of them constitutes the difference of 

 sex. It is only by the union of these two kinds of products that a new 

 cat can be formed, and the process by which that formation takes place 

 after such a union has been effected, is the process of development, the 

 consideration of which will occupy us in the next chapter but one. 



But although the process of development will there be considered, 

 the nature of generation may be more fitly spoken of here. The 

 process of growth has been already many times referred to, and 

 even in the second chapter facts as to the growth of epithelial cells, 

 of cartilage and bone, were brought before the reader's notice ; and 

 in the chapter on the organs of circulation, we saw how lymph 

 corpuscles grow by spontaneous self-division within the substance of 

 the lymphatic glands. In all these processes of growth, we have, 

 indeed, already become acquainted with a sort of reproduction, for 

 it is by the reproduction of the component cells of the various tissues 

 that their growth is effected. The fact then of an organ secreting 

 cells which detach themselves in order to perform special functions, 

 is a fact which has now no novelty for us. Indeed we have met 

 with a truly complex form of reproduction, in the development 

 from the milk-tooth's sac of a bud or off-shoot, capable of growing 

 into the permanent dental structure by which such milk-tooth is 

 ultimately replaced. Nevertheless, although generation may be 

 said to be a kind of growth ; yet it is a very special and peculiar 

 kind of growth. By it in the first place is formed a cell capable by 



