354 



THE AMERICAN NATURALIST 



[Vol. LIII 



nal factors, of the haphazard sort which operate in the 

 realms of geography and meteorology; while individual 

 development appears to be swayed chiefly by internal 

 factors, and to pursue its preordained course in a high 

 degree independent of the outside world. 



But where in all this is the necessity for preformation? 

 That two specific types of protoplasm, under identical 

 conditions of environment, will give rise to widely differ- 

 ent organisms implies, of course, considerable difference 

 in the protoplasms. It does not, however, compel us to 

 believe in the existence of correspondingly numerous dif- 

 ferences in the two cases. A single initial difference be- 

 tween two physico-chemical systems may determine a 

 multitude of differences at the end. For example, the 

 presence or absence of a certain amount of annual rain- 

 fall on a given area of the earth's surface would deter- 

 mine the nature of an indefinite number of other charac- 

 teristics, both geographical and biological. We do not 

 in this case endeavor to pick out a particular element of 

 the cause to account for each particular element in the 

 effect, Driesch's assumption that any ''mechanical" 

 {i. e., non-vitalistic) conception of the developing organ- 

 ism must be based on a preformation of parts may once 

 more be dismissed as untenable. 



Some preformation there is to be sure. Kecent Men- 

 delian studies, particularly the investigations of sex de- 

 termination, make it highly probable that certain adult 

 characters, though perhaps in no case single anatomical 

 structures, are represented by spatially separated parti- 

 cles in the nucleus. Furthermore, a certain amount of 

 "promorphology" has been demonstrated in the cyto- 

 plasm of the unfertilized egg, though this is perhaps to 

 be regarded as representing merely an early stage in 

 individual development. I feel bound to express the be- 

 lief, however, that many recent students of Mendelian 

 inheritance have carried their factorial speculations far 

 beyond the evidence, and that their detailed localization 

 of representative particles may prove in the future to 

 have more interest for psychology than for genetics. We 



