78 FIN-KAYS Ix\ CLASSIFICATION OF FISHES. 



gxee of morphological differeutiatiou of the fins, or tire approximate ex- 

 tent of <!epiirture from the i)rimitive type in reference to this one feat 

 nre. The grou])s indicated by the mark t are those in which true in 

 terradial spaces are developed, these being the least prominent in the 

 Chondrostei, wliich therefore depart least from the still more primitive 

 Dipnoi. Objections may be raised as to the plan of this diagram as in- 

 dicating relations, but it seems to me to be far more in keeping with 

 legitimate scientific method to refrain from indicating phyletic relations 

 until our knowledge is comprehensive enough to include an analysis of 

 all the characters of a series of groups, so as to be able to represent 

 their true relations. This diagram aims only to illustrate the relations 

 which ai)pear to subsist between ten of the major groups of fishes, as 

 indicated bj^ the development and morphology of the fins and fin-rays. 



The Kays have been ])laced higher than the Sharks in the diagram 

 because tlieir horn-fibers or actinotrichia are degenerate in the paired 

 fins and their organization otherwise specialized. If, however, I were 

 to consult the mode of outgrowth of the other elements of the paired fins 

 in the Eays, during which these organs maintain their primordial rela- 

 tions to a greater extent than in other Elasmobranchs, I would be 

 obliged to rank them much lower than the Sharks. If, therefore, we 

 take development as a guide, we are often forced to admit that one set 

 of organs has advanced in organization or has remained stationary, or 

 even may have become more or less degenerate and thus reverted in 

 that feature to an older and more embryonic type. The question 

 which then arises in estimating the value of such characters in tax- 

 onomy is in which one of these three ways the characters of the forms 

 under consideration have arisen. 



This is not always an easy matter, as we will find if we turn for a 

 moment to the consideration of the three above-specified methods, ac- 

 cording to which single organs and groups of organs are developed in 

 some given form. 



(fl) Taking the first case, or that of advancement, we may find that a 

 process of eoolution has specialized one feature, which in turn has 

 ck'arly exerted a stunting intluence, or one of retardation, uytou another, 

 or the reverse. In this way new features arise upon which new species 

 may be founded. 



{b) In the second case no evolution, accompanied by the addition of 

 new elements of complication to already existing, fully-developed, or 

 partially degenerate organs, is taking place, and we may designate such 

 a state as one of fixity or stable cquiUbrium. Such an attained equilib- 

 rium of the working of the life forces of an organism as a whole, as is 

 shown by adult forms, enables the naturalist to discriminate species, 

 otherwise a taxonomy would be logically impossible, because there 

 could then be no such thing as species. An orderless, lawless variation 

 of organisms would then make an end of all taxonomic method. 



