September 24, 1909] 



SCIENCE 



393 



one form apparently became predominant 

 and must be regarded as the ancestor of all 

 forms of life, whether animal or vegetable, 

 viz., the nucleated cell. The almost com- 

 plete identity of the phenomena involved 

 in cell division throughout the living king- 

 dom indicates that all unicellular organ- 

 isms and all organisms composed of cells 

 have descended from a common ancestor, 

 and that the mode of its reproduction has 

 been impressed upon all its descendants 

 throughout the millions of years which 

 have elapsed since the type was first 

 evolved. The universal distribution of 

 living cells renders it practically impos- 

 sible for us to test the possibility of a 

 spontaneous abiogenesis or new formation 

 of living from non-living matter at the 

 present time. We can not imagine that all 

 the various phenomena which we associate 

 with life were attributes of the primitive 

 life stuff. Even if we had such stuff at 

 our disposal, it would be difficult to decide 

 whether we should ascribe the possession 

 of life to it, and there is no doubt that any 

 such half-way material would, directly it 

 was formed, be utilized as pabulum by the 

 higher types of organism already abound- 

 ing on the surface of the globe. 



Integration and Differentiation.— An 

 important step in the evolution of higher 

 forms was taken when, by the aggregation 

 of unicellular organisms, the lowest meta- 

 zoon was formed. In its most primitive 

 forms the metazoon consists simply of a 

 cell colony, but one in which all individ- 

 uals are not of equal significance. Those 

 to the outer side of the mass, being ex- 

 posed to different environmental advan- 

 tages from those within, must even during 

 the lifetime of the individual have ac- 

 quired different characteristics. More- 

 over, the sole aim of such aggregation 

 being to admit of cooperation by differ- 

 entiation of function between the various 



cell units, the latter become modified ac- 

 cording to their position, some cells be- 

 coming chiefly alimentary, others motor, 

 and others repi'oductive. Cooperation and 

 differentiation are, however, of no use 

 without coordination. Each part of the 

 organism must be in a position to be af- 

 fected by changes going on in distant 

 parts, otherwise cooperation could not be 

 effected. This cooperation in the lowest 

 metazoon seems to be carried out by utili- 

 zation of the sensibility to chemical stimuli 

 already possessed by the unicellular organ- 

 ism. We have thus coordination by means 

 of chemical substances ("hormones") pro- 

 duced in certain cells and carried thence 

 by the tissue fluids to other cells of the 

 body, a mechanism of communication 

 which we find even in the highest animals, 

 including man himself. To such chemical 

 stimuli we may probably ascribe the ac- 

 cumulation of wandering mesoderm cells — 

 i. e., phagocytes— in an organism such as a 

 sponge, around a seat of injury or any 

 foreign substance that has been intro- 

 duced. By this mechanism it is possible 

 for distant parts of the body to react to 

 stimulation of any one part of the surface. 

 Communication by this means is, however, 

 slow, and may be compared to the state of 

 affairs in civilized countries before the in- 

 vention of the telegraph, when messengers 

 had to ride to different parts of the king- 

 dom in order to arouse the whole nation for 

 defense or attack. 



Foresight and Co»fco?.— Increased speed 

 of reaction and therefore increased powers 

 in the struggle for existence were obtained 

 when a nervous system was formed, by a 

 modification of the cells forming the outer 

 surface of the organism. By the growth of 

 long processes from these cells a conduct- 

 ing network was provided, running 

 through all pai-ts of the body and aft'ord- 

 ing a channel for the rapid propagation of 



