GENERAL LAW OP ANIMAL FERTILITY. 593 



* sperrn-cell ' with those of a ' gcrra-cell ; ' the latter being that 

 from within which the embryo is evolved, whilst the former 

 supplies some material or influence necessary to its evolution." * 

 Amongst the lowest vegetable organisms, as in the Desmidece^ 

 the Diatomacece, and other families of the inferior Algce, these 

 cells do not appreciably differ ; and the application to them of 

 the terms " sperm-cell " and " germ-cell " is hypothetical. From 

 this point upwards, however, distinctions become visible. As 

 we advance to higher and higher types of structure, marked 

 differences arise in the character of these cells, in the organs 

 evolving them, and in the position of these organs, which are 

 finally located in separate sexes. Doubtless a separation in the 

 functions of " sperm-cell " and " germ-cell " has simultaneously 

 arisen. That change from homogeneity of function to hetero- 

 geneity of function which essentially constitutes progress in 

 organization may be assumed to take place here also ; and, 

 indeed, it is probable that the distinction gradually established 

 between these cells, in origin and appearance, is merely significant 

 of, and consequent upon, the distinction that has arisen between 

 them in constitution and office. Let us now inquire in what this 

 distinction consists. 



If the foundation of every new organism be laid by the com- 

 bination of two elements, we may reasonably suspect that these 

 two elements are typical of some two fundamental divisions of 

 which the new organism is to consist. As nothing in nature 

 is without meaning and purpose, we may be sure that the 

 universality of this binary origin, signifies the universality of a 

 binary structure. The simplest and broadest division of which 

 an organism is capable must be that signified. What, then, 

 must this division be ? 



The proposed definition of organic life supplies an answer. 

 If organic life be the co ordination of actions, then an organism 

 may be primarily divided into parts whose actions are co-ordi- 

 nated, and parts which co-ordinate them— organs which are 

 made to work in concert, and the apparatus which makes them 

 so work — or, in other words, the assimilative, vascular, excretory, 

 and muscular systems on the one hand, and the nervous system 

 on the other. The justness of this classification will become 

 further apparent, when it is remembered that by the nervous 

 system alone is the individuality established. By it all parts are 

 made one in purpose, instead of separate ; by it the organism is 

 rendered a conscious whole — is enabled to recognise its own 

 extent and limits ; and by it are all injuries notified, repairs 

 directed, and the general conservation secured. The more the 

 nervous system is developed, the more reciprocally subservient do 



* Frin. of Phf/s., p. 907. 



