300 THE AMERICAN MONTHLY [Oct. 



the single cell thus formed, like the amoeba, divides into 

 two, and these into four and so on, but unlike the amoeba 

 all the cells remain together. Within this cellular mass, 

 as if by an unseen builder, the cells are deftly arranged 

 in their place, some to form brain, some heart, some the 

 digestive tract, others for movement, so that finally from 

 the simple mass of cells, originally so alike, arises the 

 complex organism, fish or bird, beast or man. How 

 perfectly the word offsipring describes the life process in 

 the production of this new being! That the child should 

 resemble both father and mother is thus made intel- 

 ligible, for it is a part of both. Yes, further, it may 

 resemble grandfather or great grandfather or mother, 

 for truly it is a part of them, their life conserved and 

 continued. There is no new life, it is only a continua- 

 tion of the old: ' Omne vivitm ex vivo,' all life from life. 

 But the demonstration of this prime fact required a 

 microscope, and it is an achievement of the last half of 

 this century. How counter this statement still is to the 

 common belief of mankind we may perhaps better ap- 

 preciate if we recall our own youth, and remember with 

 what absolute confidence we expected the stray horse- 

 hairs we had collected and placed in water to turn into 

 living snakes. The belief that it is an every-day occur- 

 rence for living beings to arise from lifeless matter was 

 not by any means confined to those uneducated in bio- 

 logy. It was held by many scientific men within the 

 memory of most of us. Indeed, this goblin of Spontan- 

 eous generation, even for the scientific world, has been 

 laid low so recently that the smoke of battle has scarcely 

 yet cleared from the horizon. 



In the complex body of animals, as stated above, the 

 constituent elements perform different functions. Is 

 there any hint of the way in which the action is accom- 

 plished? Let us glance at two systems, the nervous and 

 the glandular, widely different in structure and function. 



