DEVELOPMENT. 17? 



I f now, from this same point of view, we consider the rela- 

 tion borne to its environment by any superior organism in 

 its successive stages, we find an analogous series of con- 

 trasts. Of course in respect of degrees of structure the 

 parallelism is complete. The difference, at first small, be- 

 tween the little-structured germ and the little-structured in- 

 organic world, necessarily becomes greater, step by step, as 

 the differentiations of the germ become more numerous and 

 definite. How of form the like holds is equally mani- 

 fest- The sphere, which is the point of departure common to 

 all organisms, is the most generalized of figures ; and one that 

 is, under various circumstances, assumed by inorganic matter. 

 But as it develops it loses all likeness to inorganic objects in 

 the environment ; and eventually becomes distinct even from 

 nearly all organic objects in its environment. In 

 specific gravity the alteration, though not very marked, is still 

 in the same direction. Development being habitually accom- 

 panied by a relative decrease in the quantity of water and an 

 increase in the quantity of constituents that are heavier 

 than water, there results a small augmentation of relative 

 weight. In power of maintaining a temperature above 

 that of surrounding things, the differentiation from the en- 

 vironment that accompanies development is marked. All 

 ova are absolutely dependent for their heat on external 

 sources. The mammalian young one is, during its uterine 

 life, dependent on the maternal heat; and at birth has 

 but a partial power of making good the loss by radiation. 

 But as it advances in development it gains an ability to 

 maintain a constant temperature above that of surrounding 

 things: so becoming markedly unlike them. Lastly, 

 in self-mobility this increasing contrast is no less decided. 

 Save in a few aberrant tribes, chiefly parasitic, we find the 

 general fact to be that the locomotive power, totally absent 

 or very small at the outset, increases with the advance 

 towards maturity. The more highly developed the organism 

 I ' ' 



