82 THE VOYAGE OF H.M.S. CHALLENGER. 



Classification of Sponges. 



The principles of classification have assumed in modern zoology a general importance 

 previously unknown, since we maintain that these principles are essentially phylogenetical, 

 that morphological relation in a certain sense is historical, and that a true natural 

 system approaches to the hypothetical pedigree of the related forms. The class of 

 sponges possesses in this respect a particular interest, because they are the lowermost 

 among the Metazoa, the simplest in organisation, and the most variable as regards 

 constancy of species. Led by this conviction, I began in 1867 my researches on the 

 Calcispongise, the results of which were published in 1872 in my Monograph of this 

 order. 



The general principles of classification there given are in accordance with those which 

 have been employed in three excellent Monographs among the five Reports hitherto 

 published on the sponges collected by the Challenger Expedition. W. J. Sollas in his 

 Report on the Tetractinellida, 1 F. E. Schulze in his Report on the Hexactinellida, 2 and 

 S. 0. Ridley and A. Dendy in their Report on the Monaxonida, 3 have expressed opinions 

 and followed principles in the classification of the Spongias which are essentially the 

 same as my own. But the same cannot be said of two other reports on sponges 

 belonging to this series, viz., those which Dr. Polejaeff has published on the Calcarea 4 and 

 on the Keratosa. 6 Since my own researches concerned just these two groups, and since 

 my general statements are severely attacked by Dr. Polejaeff, I may be permitted here 

 to add some remarks on his opposing views, and to explain the contradictions in our 

 systematical aims. 



Polejaeff has explained his systematical principles not only in the two Reports above 

 mentioned, but also in the general account of his chief results communicated in the 

 Narrative of the Cruise of H.M.S. Challenger. 6 His first and foremost principle is, that a 

 natural classification of the sponges, hitherto wanting, can only be reached by comparative 

 physiology. " So long as spongiology will not attach due influence to comparative 

 physiology in its systematic proceedings, no hopes can be entertained of a natural 

 arrangement of the sponges." 7 The most important part of a natural systematic 

 classification, according to Polejaeff, consists in the task of proving actually which of the 

 so-called genera and subgenera " are really to be regarded as subgenera (i.e., groups 

 which, although connected by numerous intermediate stages with their systematic- 

 neighbours, still present in their organisation a new principle fit for a further 

 development) and not as species and even varieties. This latter question is to be decided 

 (perhaps exclusively) by the methods of comparative pl^siology." 8 Polejaeff also 



1 Zool. Chall. Exp., pt. lxiii. vol. xxv. p. cv. 2 Zool. Chall. Exp., pt. liii. vol. xxi. p. 485. 



3 Zool. Chall. Exp., pt. lix. vol. xx. p. 53. 4 Zool. Chall. Exp., pt. xxiv. vol. viii. 



6 Zool. Chall. Exp., pt. xxxi. vol. xi. 6 Narr. Chall. Exp., vol. i. p. 639. 



7 Loc. cit., p. 643. • 8 Loc. cit., p. 644. 



