2G2 THE INDUCTIONS OF BIOLOGY. 



these are but incipient : individual ectoderm cells have mus- 

 cular processes. Xor is there any " special aggregation of 

 nerve-cells/' If any stimulating units exist they are 

 scattered. But in the Mediisa-siaige nerve-matter is collected 

 into a ring round the edge of the umbrella. That is to say, 

 in the undeveloped form such motor action as occurs is not 

 effected by a specialized part which excites another part; 

 but in the developed form a differentiation of the two has 

 taken place. All higher types exhibit this differentia- 

 tion. Be it muscle or gland or other operating organ, the 

 cause of its activity lies not in itself but in a nervous agent, 

 local or central, with which it is connected. Hence, 

 then, there is congruity between the above interpretation 

 and certain general truths displayed by animal organization 

 at large. We may infer that in a way parallel to that just 

 indicated, cell-evolution was, under one of its aspects, a 

 change from a stage in which the exciting substance and the 

 substance excited were mingled with approximate uniformity, 

 to a stage in which the exciting substance was gathered 

 together into the nucleus and finally into the chromosomes: 

 leaving behind the substance excited, now distinguished as 

 cytoplasm. 



■§ 74/. Some further general aspects of the phenomena 

 appear to be in harmony with this interpretation. Let us 

 glance at them. 



In Chapters III and IIIa of the First Part, reasons were 

 given for concluding that in the animal organism nitroge- 

 nous substances play the part of decomposing agents to the 

 carbo-hydrates — that the molecular disturbance set up by 

 the collapse of a proteid molecule destroys the equilibrium 

 of sundry adjacent carbo-hydrate molecules, and causes that 

 evolution of energy which accompanies their fall into mole- 

 cules of simpler compounds. Here, if the foregoing argu- 

 ment is valid, we may conclude that this highly complex 

 phosphorized compound which chromatin contains, plays the 



