344 The Morality of Nature 



veloped. And later again another difference arises. There 

 were some creatures which developed the gastrula form by 

 first forming a hollow sphere, and then turning one half of 

 it into the other half so that the structure not only had a bell 

 hollow, but a shell of the bell which was hollow; and some 

 of these creatures budded inside the hollow shell so that 

 when the egg issued from that first protection it was not 

 emitted entirely but was lodged in the bell. Obviously such 

 creatures were able to adapt this second lodgment and to 

 make a second type of preserved environment, in which the 

 egg might fully develop through its final marine stages of 

 growth, without any return to the water at all; and with- 

 out the limitations of the helpless stage of the independent, 

 yet dormant egg. 



Some of these creatures were able to become entirely ter- 

 restrial, and at the same time to remain viviparous, and to 

 enjoy in their early stages those facilities for development 

 of offspring which mark the mammalian animals, and dis- 

 tinguish them from those others whose late development is 

 perforce in a natural environment where accidental qualities 

 are many and the constant qualities few. Thus we find 

 heredity, fixed by a conservation of ancient environment, 

 still liable to variation in changing circumstances, but un- 

 changed so long as those circumstances remain constant. A 

 germ-plasm therefore reproducing accurately and inevitably 

 the highly organized heredity structure of a race, does so, 

 not by fettering its substance with absolutely controlling 

 atoms, but by preserving in its somatic body, not only the 

 life-plasm which made it, but also the conditions under 

 which it formerly arose. 



