358 THE ZOOLOGIST. 



no such iron-bound categories and absolute distinctions. For in- 

 stance, if we compare the organs of one and the same individual, we 

 at once observe repetition, e.g. that of serial homology, which implies 

 many difficulties, with very different interpretations. Even in such 

 an apparently simple case as the relation between shoulder girdle 

 and pelvis we are at a loss, since the decision depends upon our view 

 as to the origin of the paired limbs, whether both are modified visceral 

 arches, and in this case serially repeated homogenes, or whether they 

 are the derivatives from one lateral fin, which is itself a serial com- 

 pound, from which, however, the proximal elements, the girdles, are 

 supposed to have arisen independently. What is metamerism ? Is it 

 the outcome of a process of successive repetitions so that the units 

 are homogenes, or did the division take place at one time all along 

 the line, or is it due to a combination of the two procedures ? 



The same vagueness finds its parallel when dealing with the cor- 

 responding organs of different animals, since these afford the absolute 

 chance that organs of the same structure and function may not be 

 reducible to one germ, but may be shown to have arisen indepen- 

 dently in time as well as with reference to the space they occupy in 

 their owners. As heterogenes they can be compared as to their 

 causes. In the study of the evolution of homogenes the problem 

 is to account for their divergencies, whilst the likeness, the agree- 

 ments, so to speak, their greatest common measure, is eo ipso taken 

 to be due to inheritance. When, on the contrary, dealing with 

 heterogenes we are attracted by tbeir resemblances, which, since they 

 cannot be due to inheritance, must have a common cause outside 

 themselves. Now, since a leading feature of the evolution of homo- 

 genes is divergence, whilst that of heterogenes implies convergence 

 from different starting-points, it follows that the more distant are 

 these respective starting-points (either in time or in the material) the 

 better is our chance of extracting the greatest common measure out 

 of the unknown number of causes which combine in the production 

 of even the apparently simplest organ. 



These resemblances are a very promising field and the balance of 

 importance will more and more incline towards the investigation of 

 Function, a study which, however, does not mean mere physiology 

 with its present-day aims in the now tacitly accepted sense, but that 

 broad study of life and death which is to yield the answer to the 

 question Why ? 



Meantime, comparative anatomy will not be shelved ; it will 

 always retain the casting-vote as to the degree of affinity among 

 resemblances, but emphatically its whole work is not to be restricted 

 to this occupation. It will increasingly have to reckon with the 

 functions, indeed, never without them. The animal refuses to yield 

 its secrets unless it be considered as a living individual. It is true 

 that Gegenbaur himself was most emphatic in asserting that an 

 organ is the result of its function. Often he held up to scorn the 

 enibryographer's method of muddling cause and effect, or he merci- 

 lessly showed that in the reconstruction of the evolution of an organ 

 certain features cannot have been phases unless they imply physio- 



