352 COMPARATIVE ANATOMY 



lusks, not on the antennules, but on the telson. This situation pre- 

 vents our homologizing them with the antennulary statocysts of 

 the other crustaceans, and the difference in phyletic origin prevents 

 homologizing them with those of the mollusks, the worms, or the 

 ccelenterates. Is not a fundamental conformity so profound, between 

 organs phylogenetically distinct, quite as remarkable a thing as the 

 resemblance of origin revealed by embryology between two organs 

 the structure and functions of which are very different? 



Is it right, then, to place the latter in the holy tabernacle of homo- 

 logies in order to prostrate ourselves before it, while we relegate 

 the former to the despised chaos of analogies? 



But, some one says, comparisons must nevertheless have a sanc- 

 tion, and homologies must be distinguished from analogies. 



That may be, but there is no need to sacrifice the one to the 

 other. 



Let us return to the case of Asterias and Asterina. 



When we have proved and noted that the mouth of the one does 

 not proceed from the same point of the larva as does that of the 

 other, we have given to embryology all that it has a right to claim, 

 and it is only just to render to anatomy what it has a right to 

 demand in declaring that in all other respects the mouth of Asterias 

 and that of Asterina are identical. 



In the presence of these divergences, shall we clash with embryo- 

 logy in proclaiming an homology w r hich it rejects, or torture anatomy 

 in denying an homology which the latter claims? The simplest 

 thing is to clash with or torture nothing by saying nothing. 



Where is the necessity of formulating a general proposition which 

 shall certainly be false on a certain side, when it is possible to sepa- 

 rate it into two true propositions, in saying that the mouth of 

 Asterias and that of Asterina are similar in all respects except that 

 they are not homogenic. 



But, some one says, that is what we do when we declare that the 

 two mouths are not homologues, since by definition homology is 

 nothing else than phyletic homogeny. 



That would be true if we held scrupulously to that definition; 

 but as a matter of fact, in the search for homologies we turn to all 

 possible characteristics, even at times to physiological ones, for- 

 bidden though they are. We must many times reduce homology 

 to the modest significance of homogeny. 



Homology has become and will remain in biological language 

 the mark of an important, fundamental resemblance, reducing to a 

 subordinate and superficial significance and to a secondary interest 

 whatever differences there may be. 



There are words which are to ideas what infectious microbes are 

 to the body. Such, in the science of evolution, are " tendencies of 



