270 ANIMAL MORPHOLOGY 



lation, for example. It can be much less close when it acts with 

 reference to parts adapted to very distinct roles, organs of locomo- 

 tion and the digestive apparatus, or better the tegumentary system 

 and the skeleton, etc. 



But the independence is especially great if we consider on the one 

 hand the organs which subserve the life of the individual and on 

 the other those which are destined to insure the perpetuation of the 

 species. 



The soma and the gonads, to employ modern expressions which 

 designate these tw r o totalities, are in a certain sense two organisms, 

 which are juxtaposed or incased the one in the other, whose devel- 

 opment may proceed very unequally, although any modification 

 effected in one has in general an influence upon the other. 



It is because of their reliance upon this notion fundamentally 

 exact, but exaggerated and enveloped with a metaphysical atmo- 

 sphere, that the partisans of the ancient theory of evolution (pre- 

 existence and germinal localization, preformation of the embryo) 

 have for a long time struggled against the ideas of C. F. Wolff. 



In following the same line of thought more recently, A. Weismann 

 has sought to construct his well-known theories upon the assump- 

 tion of the non-transmissibility of acquired characters. 



Finally, it is the same consideration which, when extended to the 

 first phases of embryology, to different cellules of the morula and even 

 to different regions of the unsegmented egg, has served as the basis of 

 the mosaic theory of W. Roux, which has since been so ingeniously 

 modified by E. B. Wilson. 



While adhering to the strict observation of facts easiest to verify, 

 we shall call only that epigenesis which, in revealing to us the pos- 

 sibility of a vital concurrence between the organs and even between 

 the plastids which constitute multicellular beings, permits us to 

 explain easily all the complex facts of evolutionary polymorphism; 

 progenesis, neotenie, dissogonie, poecilogonie , and in general the curious 

 peculiarities of development that since Chamisso and Steenstrup we 

 have grouped under the very improper name of alternate generations 

 or of geneagenesis (de Quatrefages). 



There is thus established a vast array of information which is suffi- 

 ciently extended to constitute to-day a new branch of morphology 

 which we may call genesiology. 



The object of genesiology is the study, both descriptive and experi- 

 mental, of different evolutionary modes. 



In the preceding pages we have at different times spoken of experi- 

 ments and of the experimental method in a sense different from that 

 which is often given to these words by the physiologists of the old 

 school. This is the place perhaps to indicate the manner in which we 

 understand the introduction of experimentation into the morpholog- 



