104 THE WHENCE AND THE WHITHER OF MAN 



special system of tubes lias developed to carry the nu- 

 triinent, and usually oxygen also, needed to keep up 

 the combustion required to furnish the energy in these 

 active organs. The digestive system has attained its 

 definite form with the appearance of an anal opening 

 and the accompanying division of labor and differen- 

 tiation into fore-, mid-, and hind-intestine. 



The digestive and reproductive systems have thus 

 nearly attained their final form. From the higher 

 worms upward the digestive system will improve 

 greatly. Its lining will fold and flex and vastly increase 

 the digestive and absorptive surfaces. The layer of 

 cells which now secrete the digestive fluids will in part 

 be replaced by massive glands. Far better means of 

 grasping food than the horny teeth of annelids will yet 

 appear. But all these changes are inconsiderable com- 

 pared with the vast advance made by the muscular 

 and nervous systems. Reproduction and digestion 

 are losing their supremacy in the animal body. Their 

 advance and improvement will require but little further 

 attention. 



In the annelid especially, and to some extent in the 

 schematic worm, the supra - cesophageal ganglion is 

 relieved in part of the direct control of the muscular 

 fibrils and has become an organ of perception and the 

 seat of government of lower nervous centres. In all 

 higher forms it innervates directly only the principal 

 sense-organs of the head. And at this stage the light- 

 perceiving directive eye has developed into a form-per- 

 ceiving, eidoscopic organ. The eye was short of range 

 and its images were perhaps rude and imperfect, but 

 it was a visual eye and had vast possibilities. The 

 animal is taking cognizance of ever more subtle ele- 



