298 THE INDUCTIONS OF BIOLOGY. 



Here, too, may fitly be pointed out the fact tliat, by 

 " natural selection/' there will in every case be produced the 

 most advantageous proportion of males and females. If the 

 conditions of life render numerical inequality of the sexes 

 beneficial to the species, in respect either of the number of 

 the offspring or the character of the offspring; then, those 

 varieties of the species which approach more than other 

 varieties towards this beneficial degree of inequality, will be 

 apt to supplant other varieties. And conversely, where 

 equality in the number of males and females is beneficial, 

 the equilibrium will be maintained by the dying out of such 

 varieties as produce offspring among which the sexes are not 

 balanced. 



XoTE. — Such alterations of statement in this chapter as 

 have been made necessary by the advance of biological know- 

 ledge since 1864 have not, I think, tended to invalidate its 

 main theses, but have tended to verify them. Some expla- 

 nations to be here added may remove remaining difficulties. 



Certain types, which are transitional between Protozoa and 

 Metazoa, exhibit under its simplest form the relation between 

 self-maintenance and race-maintenance — the integration 

 primarily effecting the one and the disintegration primarily 

 effecting the other. Among the Mycetozoa a number of 

 amoeba-like individuals aggregate into what is called a 

 Plasmodium; and while, in some orders, they become fused 

 into a mass of protoplasm through which their nuclei are 

 dispersed, in other orders (Sorophora) they retain their indi- 

 vidualities and simply form a coherent aggregate. These 

 last, presumably the earliest in order of evolution, remain 

 united so long as the plasmodium, having a small power of 

 locomotion, furthers the general nutrition; but when this 

 is impeded by drought or cold, there arise spores. Each 

 spore contains an amoeboid individual; and this, escaping 

 when favourable conditions return, establishes by fission and 

 by union with others like itself a new colony or plasmodium. 



