280 ANIMAL MORPHOLOGY 



preceded them, and foresees to a certain extent the transformations, 

 undoubtedly less extended, which the forms, still possessed at 

 present of a certain plasticity, will undergo in the future. 



At all events, in pretending that the morphologist plays the r61e 

 of creator, we do not intend to affirm that he could, as the adver- 

 saries of the evolutionary theory have sometimes demanded with 

 ridiculous unreasonableness, transform hie et nunc one animal species 

 into another species through a simple modification of food and me- 

 dium, and, for example, produce the ox from the sheep by placing 

 the latter for some generations in especially favorable conditions. 

 Such a result would be the negation of the Darwinian doctrine itself, 

 which, we know, makes great use of modifications accumulated 

 by heredity and irrevocably fixed in definitely established organisms. 



What the morphologist is able to attempt, and what in fact he 

 does attempt, is to discover and to analyze the small variations 

 which are determined by primary factors, and to determine thus 

 how by a slow summation these variations, at first insignificant, 

 are united to give origin, either by a continuous or by an apparently 

 discontinuous process, to the much more evident characters which 

 separate species. 



I do not dare even to believe, with some bold pioneers of modern 

 science, that the most perfect knowledge of the auto-regulation of 

 organisms will perhaps permit us to modify these auto-mechanisms 

 and to obtain thus a rapid variation of animals and plants. 1 



After a series of innumerable transformations of which it is 

 sometimes possible to discover some traces in the form of fossil 

 impressions in the depths of the earth, the majority of living beings 

 have arrived at a relatively stable state of equilibrium. They have 

 exhausted the possibilities of what I have called their plastic poten- 

 tial, they are able to effect only feeble oscillations about a mean 

 position, and no considerable change in the ethological conditions, 

 in general, can be compensated for by a new arrangement of regu- 

 lative reaction. 



And even for those which still have a reserve of plasmatic elas- 

 ticity sufficient to permit of new adaptations, we must not forget 

 that they can develop only in a certain number of well-defined 

 directions, and that we must always bear in mind two essential facts 

 which regulate the transformations which are hereafter possible: 



' ' So far as I am aware no one has vet found a method of bringing about a rapid 

 variation in animals or plants. I am inclined to believe that this failure is at least 

 partly due to the existence of mechanisms of regularisation. . . . We again meet 

 with two possibilities: we shall either succeed by a series of continued slight 

 changes in one and the same form in bringing about a large transformation from 

 the original form, or we shall obtain the result that in each form the possibility 

 of evolution is limited, and that at a certain point the constancy of a species is 

 reached." J. Loeb, The Limitation of Biological Research (University of California 

 ublications, Physiology, vol. i, no. 5, Oct. 1903). 



