102 THE WHENCE AND THE WHITHEB OF MAN 



of epidermis; only tliese layers in hydra possess 

 powers lost to the corresponding cells of our bodies in 

 the process of differentiation. Notice, please, that 

 when cell or organ has once been developed it persists, 

 as a rule, modified, but not lost. Nature's experiments 

 are not in vain ; her progress is very slow but sure. 

 But hydra has also the promise of better things, traces 

 of muscular and nervous tissue. There are still no 

 compact muscles, like our own, much less ganglion or 

 brain or nerve-centre of individuality. The tissues 

 are diffuse, but they are the materials out of which the 

 organs of higher animals wiU crystallize, so to speak. 

 Notice also that these higher muscles and nerves are 

 here entirely subservient to, and exist for, digestion and 

 reproduction. 



In the turbellaria the reproductive system has 

 reached a very high grade of development. It is a 

 complex and beautifully constructed organ. The di- 

 gestive system has also vastly improved ; it has its 

 own muscular layers, and often some means of grasping 

 food. But it is slower in reaching its full develop- 

 ment than the reproductive system. But all the mus- 

 cles are no longer attached to the stomach ; they are 

 beginning to assert their independence, and, in a rude 

 way, to build a body-wall. But they are in many lay- 

 ers, and run in almost all directions. Some of these 

 layers wiU disappear, but the most important ones, 

 consisting of longitudinal and transverse fibres, wUl 

 persist in higher forms. Locomotion by means of 

 these muscles is slowly coming into prominence. They 

 are no longer merely slaves of digestion. 



But a muscular fibril contracts only under the stimu- 

 lus of a nervous impulse. More nerve-cells are neces- 



