136 HABIT AND INTELLIGENCE. [chap. 



and ex- the whole substance of some of the lowest organisms 

 parts uni- ^^^^^^'^^^o ^^ore consolidated on the outside than in the 

 versal. inside. Thus are produced the single cells of which, 

 consist the Diatomaceae among plants, and the Gromia 

 among animals ; and there is probably no organism, not 

 even the Amoeba, which does not present this character 

 in some degTee. The higher organisms, as already stated, 

 consist (at least in great part) of masses of variously- 

 modified cells ; and in them the external cells are usually 

 External condensed into a comparatively denser and sometimes 

 f^ctive.'^° hard tissue, the function of which is to protect the interior 

 organs ; while the tissues of the interior, where the vital 

 processes go on, continue soft. So that in the highest 

 organisms and in the lowest alike tbe exterior parts are 

 consolidated, in order to protect the interior parts and hold 

 them together. 

 Separation The next distinction that we meet in the ascending 

 tiveandi-e- scale of natu^re is that into the nutritive and reproductive 

 productive organs : in other words, into the organs which minister to 

 universal, the life of the organism itself, and those which provide for 

 the existence of future organisms of the same kind. This 

 distinction is not absolutely universal among organisms : 

 among the Diatomaceae and Desmidefe, which are very simple 

 forms of Algse, the whole organism is capable of acting as 

 a reproductive organ, in a way to be hereafter described ; 

 besides that many, probably all, of the lowest vegetables 

 and animals alike propagate their race by spontaneous 

 division into parts, a characteristic from which the Diato- 

 maceae have their name, 

 and not It is important to observe that the distinction between 



mental ^^^® nutritive and the reproductive functions is not funda- 

 mental. The reproductive function is only a particular 

 form of the nutritive. Reproduction essentially consists, 

 as already stated, in separating from the organism a small 

 portion of formative material, or germinal matter, under 

 such, circumstances as to enable it to build up a completely 

 new organism. But the properties of the germinal matter 

 which is thus detached for the formation of a new organism 

 do not essentially differ from the properties of the germinal 



