5O ELEMENTS OF BIOLOGY. 



forth in the several parts of the two organisms will be nearly 

 or exactly alike." For agreements produced in this way the 

 term "homoplasy" is proposed. 



Two very strong objections seem to render the acceptance 

 of these terms inadmissible. As regards the term " homo- 

 geny," as above defined, it is to be remarked that its value 

 depends wholly and solely upon the value which may be 

 attached to the hypothesis of " evolution." Many authori- 

 ties of no small weight do not accept this hypothesis, and 

 to such the term " homogeny " is worse than useless, for it 

 implies a relationship between "homologous" organs, in 

 which they do not believe. For general use, therefore, we 

 must prefer the term " homologous " to that of "homogene- 

 tic." In the second place, as regards the term " homo- 

 plasy," a reference to the above definition will show that it 

 is proposed for those resemblances which are produced in 

 parts or organs of the same animal, or of different animals, 

 by identical forces or environments, the said parts being 

 nearly or exactly alike to begin with. If, however, the 

 " homoplastic " parts are primarily alike before they begin 

 to be acted upon by similar forces, then they would seem to 

 be "homogenetic ;" and no fresh term is required to indi- 

 cate the fact that similar conditions acting upon parts sub- 

 stantially the same will produce similar results. No attempt 

 is made to explain how the parts in question come to be 

 "nearly or exactly alike" in the first instance; and, in the 

 absence of such an explanation, it seems clear that it is a 

 mere assumption that the likeness which we at present 

 observe between them is only the result of the action of 

 " identical or nearly similar forces." 



III. HOMOMORPHISM. Many examples are known, both 

 in the animal and the vegetable kingdom, in which families 

 widely removed from one another in their fundamental 

 structure, nevertheless present a singular and sometimes 

 extremely close resemblance. For this phenomenon the 

 term "homomorphism " has been proposed, and such forms 



