REPORT ON THE DEEP-SEA KERATOSA. 83 



concludes his Report on the Keratosa with general considerations on the systematic 

 importance of comparative phj'siology, which, according to him, shall solve the difficult 

 problems that no morphological science, neither comparative anatomy nor comparative 

 ontogeny, may be able to solve. 



My own systematic principles, based on classificatory work of thirty years, and 

 practically employed in my General Morphology (1866), as well as in my Monographs of 

 the Radiolaria, Calcispongias, Medusae, and Siphonophorae, start from quite an opposite 

 point of view. My firm conviction is, that every systematic task can be solved only by 

 morphological, not by physiological work. I cannot find, in the immense systematic 

 literature of zoology and botany, a single work in which any important progress has 

 been made by the help of comparative physiology ; I cannot even understand in what 

 possible way this science should be useful. All classificatory works, clearing our views 

 on the natural system of major or minor groups, are based only upon morphological 

 researches either of comparative anatomy (in the widest sense) or of comparative 

 ontogeny and palaeontology. Morphology and physiology, the two main branches of 

 biological science, are of equal value and equal importance, but their methods and aims 

 are totally different, and in systematic work, in the distinction and phylogenetic 

 arrangement of forms, morphology alone is applicable, not physiology. Dr. Polejaeff 

 himself, although so emphatically praising the latter, has in his classification employed 

 only the former ; he has not demonstrated the way in which classification shall be 

 elucidated by comparative physiology. 



The second important point in which my systematic views are quite opposed to those 

 of Dr. Polejaeff, is the true meaning and the proper signification of the systematic 

 categories, or of the larger and smaller groups of forms, which are distinguished in each 

 system as classes, orders, families, genera, species, varieties, &c. Two different and 

 opposite conceptions are possible in this respect : either all these categories are artificial 

 and of only relative value, divisions produced by the logical mind of the systematic 

 naturalist, or they are all natural and possess an absolute character, founded on their 

 morphological differences and justifying their absolute distinction. We may briefly call 

 this latter the dogmatic conception, the former the critical conception of the systematic 

 categories. 



The dogmatic conception, supported by Dr. Polejaeff, has been explained in the most 

 ingenious manner by Louis Agassiz, in his well-known essay on classification (1859). 

 He undertook the task of giving an absolute definition to each of the systematic 

 categories, and to prove that they are distinct not only in a relative and quantitative 

 respect, but also in an absolute and qualitative respect. I have given a careful critical 

 analysis of these views in chapter xxiv. of my General Morphology. 1 I have stated 

 there that each absolute definition of any category, in the sense of L. Agassiz, is perfectly 



1 Generelle Morphologie, vol. ii. pp. 374-402. 



