PRESENT TENDENCIES OF MORPHOLOGY 269 



relation to bionomic conditions and as a necessary consequence of the 

 life which their ancestors had to lead. 



Not less interesting, it seems to me, are the embryological pecul- 

 iarities that I have brought together under the name " poecilogonie." 

 Two beings belonging to the same species as like as possible in the 

 adult stage, so much alike sometimes that the eye of the best-trained 

 specialist cannot detect the least difference between them, may pre- 

 sent in the series of their ontogenetic stages and even in the ovarian 

 form very marked differences, if their embryonic bionomy is not the 

 same; if, for example, the environment has not the same chemical 

 composition or if the season of development is different, or yet again 

 if the biological conditions vary with the cosmic surroundings in 

 the different habitats of a widely dispersed species, whence the terms 

 poecilogonie geographique, poecilogonie saisonniere, etc. 



What is more astonishing than these curious experiments of mor- 

 phology realized by nature, which I have formerly discussed under 

 the name of parasitic castration? And however mysterious the 

 modifying action of the indirect gonotome may be to us, is it not very 

 instructive from the morphodynamic point of view to see this para- 

 site, by action at a distance upon a host of determined sex, cause 

 the appearance of the characters of the opposite sex even when these 

 characters will have no value for the animal which possesses them? 

 Finally, this notion of a morphological complex constituted by the 

 host and its parasite acquires primary importance when. we relate 

 these parasitic complexes to the unstable biological equilibrium of 

 homophysical or heterophysical complexes in more or less perman- 

 ent equilibrium, realized either in the galls or in symbiotic forms 

 such as the lichens, plants with mycorhiza, etc. 



At most the notion of complexes of different beings associated in 

 harmonious symbiosis is only a generalization of what we observe 

 in all multicellular organisms in the course of their evolution. 



As early as the middle of the eighteenth century C. Fred. Wolff had 

 established upon a firm basis the theory of epigenesis. He showed 

 that living beings do not develop, as had been thought, at the expense 

 of a preformed rudiment, growing much as the image of an object 

 enlarges when examined successively with glasses of gradually in- 

 creasing powers of magnification. 



The different organs of an animal are formations of a relative au- 

 tonomy which work together in the construction of a whole whose 

 equilibrium is not preestablished and whose plan may sometimes be 

 modified during the course of construction. 



It is well understood that in respect to reciprocal dependence the 

 different systems of organs vary considerably. Sometimes this de- 

 pendence is very close, as when the appropriate functions of the 

 organs are themselves very closely united, respiration and circu- 



