364 THE POPULAR SCIENCE MONTHLY, 



are not differences relating to the life-characters, but merely to 

 the physical forms in which life manifests itself. 



As we know of no simpler organisms than these, and can not 

 conceive that life could manifest itself in any simpler forms, we 

 must regard them as the primordial animals — the progenitors of 

 the animal kingdom. 



The conclusion which we reach, then, is that not only all man's 

 distinctively human qualities came to him by inheritance, but also 

 all his purely animal qualities. The former came from human 

 ancestors, the latter from animal ancestors. And as with the 

 former, so with the latter ; the more specific came from ancestors 

 less remote, the more general from ancestors more remote. The 

 most general, the absolutely fundamental and essential, came from 

 the primordial living beings. 



The animals of the first life-period were succeeded by others 

 which, as we have seen, possessed not only the physiological char- 

 acters of the primordial organisms, but also certain anatomical 

 characters not received by inheritance, enabling them to carry out 

 the physiological processes more perfectly. If for the sake of sim- 

 plicity we consider the animals of the first and second life-periods 

 to be those which we have already designated as the lowest and 

 the lower animals respectively, then the latter received by inher- 

 itance from the former their functions of nutrition and reproduc- 

 tion, and acquired the special organs of alimentation and repro- 

 duction by which these functions were the better carried on. The 

 question whence these new characters came need form no part of 

 our present inquiry. For our purpose it will be sufficient to say 

 that they resulted from external causes, it being understood that 

 it is not intended to preclude the idea of the agencies in question 

 being natural causes. The fact here to be set forth is that these 

 animals of the second life-period transmitted, by the law of he- 

 redity, these characters that first appeared in them, along with 

 those which they had received by inheritance, to their descend- 

 ants. It is not to be supposed, of course, that the characters 

 were preserved unmodified as to details, but only that their gen- 

 eral nature, both as to structure and use, were retained. The 

 animals of the third life-period — which we may consider those 

 we have called the higher animals — therefore possessed at the 

 outset all the characters of the first, together with those that 

 were peculiar to the second. They, in their turn, under the in- 

 fluence of external causes, came to possess new characters — a ver- 

 tebral column, four-chambered heart, etc. — while those which 

 they had received by inheritance from their forerunners of the 

 second period attained in them a higher development ; in their 

 turn, too, they transmitted their advanced organization to the 

 succeeding order of beings— that is, to the human race. This 



