EEFORT ON THE DEEP-SEA KERATOSA. 



85 



This is not the place to answer his objections ; I may only remark, that he has not taken 

 into account the main intention of my classificatory essay, which was to prove analytically 

 the theory of descent, and to prove that so-called " bonse species " do not exist in nature, 

 that they are all originally " bad species." I have noted this principal intention in the 

 preface to my Monograph of Calcispongise (pp. xi, xii), and explained it in the second 

 part of the fourth chapter (Phylogeny, pp. 340-360). A natural consequence of my 

 phylogenetic conviction is the opinion that "natural species" do not exist, and 

 therefore the 21 genera and 111 species which I have distinguished in my "natural 

 system " can possess only a relative value. They are, indeed, more natural than those of 

 the older artificial system. Polejaeff, always looking for absolute distinction, must, of 

 course, reject them. But his own distinctions are also more or less artificial, and exposed 

 to the same general objections as all others. 



Curiously enough, Polejaeff says in the Narrative, 1 that " the whole Report on the 

 Keratosa is almost exclusively of a critical character." My own view, based upon opposite 

 principles, is that his Reports are more dogmatical than critical. For example, I must 

 regard it as perfectly dogmatical when Polejaeff unites all the Keratosa in a single 

 family and all the Asconidse in a single genus. What advantage is got by this summary 

 blending ? It would be scarcely less dogmatical to unite all the Keratosa in a single 

 genus, or all the sponges in a single family. Polejaeff strongly blames the cir cuius 

 vitrosus which most authors follow in distinguishing genera and families among the 

 sponges. 2 In my own opinion, his whole systematic work turns in a large circulus 

 vitrosus. It is based upon dogmatic convictions which are quite incompatible with our 

 modern phylogenetical views and with the first principles of the theory of descent. 



Relation of the Keratosa to the other Sponges. 



The new forms of so-called Keratosa (or Ceratina) which are described in this Report, 

 and which inhabit the abyssal regions of the deep sea, seem to throw a new light on 

 this remarkable group of sponges, and to modify somewhat our views on their relations 

 to the other Porifera. The general opinion of most modern spongiologists (maintained 

 by F. E. Schulze, Lendenfeld, Vosmaer, Sollas, and others) is, that the horny sponges or 

 Keratosa have descended from Silicosa, or from sponges which possessed siliceous spicules. 

 The uninterrupted chain which connects certain Keratosa with certain Silicosa is the 

 mainstay of this opinion. I must confess that this phylogenetical hypothesis, though 

 based on many acceptable arguments, seems to me by no means to be decidedly demon- 

 strated. The new Keratosa here described present several great difficulties to its 

 acceptance. It seems to me very improbable that all these characteristic horny sponges 

 of the deep sea (and especially the cannocoelous Ammoconidse) are degenerate Silicosa 



1 Loc. cit., p. 645. 2 Zool. Chall. Exp., pt. xxxi. p. 83. 



