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



violent manner, being brought up from depths between 2000 and 2900 fathoms to the 

 surface within a few hours. Even many deep-sea animals of much stronger texture 

 are so injured by this sudden change that their soft tissues are more or less destroyed. 

 The same must be the case in a much greater degree with such delicate tissues as the 

 epithelia of Sponges and Hydroids. 1 A natural consequence of this circumstance is the 

 fact that in all the Deep-sea Keratosa the epithelia (exodermal as well as entodermal) 

 were more or less destroyed. No trace could be found anywhere of the outer covering 

 pavement-epithelium of the exoderm. The peculiar flagellated epithelium of the 

 entoderm was not distinctly recognisable in most of the specimens, and not fitted for 

 finer examination ; in several species, however, its presence could be made out with 

 certainty. The state of preservation was generally better in the structures of the 

 mesoderm and in the skeleton. 



Families of the Keratosa. 



The numerous and very different forms of sponges, which are united by modern 

 authors under the name Keratosa or Ceratina (Horny Sponges, Hornschwamme in 

 German), are divided into a great number of genera, and these again collected into a 

 small number of families. The characters and affinities of these families must be 

 discussed here to a certain extent, seeing that only two of the four families in which I 

 have disposed the Deep-sea Keratosa agree with those of shallow water, the other two 

 being perfectly new. 



Polejaeff is the only modern author who holds that "the whole group of Keratosa 

 is nothing more than a single famdy." He expresses this singular opinion in a very 

 decisive manner, both in his Report on the Keratosa 2 and in his general notes on the 

 Horny Sponges, incorporated in the Narrative of the Cruise. 3 These conceptions of 

 Polejaeff, as also many of his other systematic views, are quite incompatible with the 

 phylogenetical principles of modern classification ; they are, in my opinion, quite 

 unnatural and dogmatical. This will be demonstrated in the remarks on classification, 

 in the Appendix to this Report. Since no other spongiologist will follow the view of 

 the Russian spongiologist, it need not be here refuted. 



Two well-known spongiologists, Lendenfeld and Vosmaer, published independently 

 in the year 1887 the Prodromus of a new sponge-system, and since their opinions agree 

 in the most important points, we may here consider together their classification of the 

 Keratosa, passing over all the former attempts, which are critically discussed in the 



1 Compare the remarks on Monocaulus by Sir Wyville Thomson, in the Report on the Hydroida by Allman 

 (Zool. Chall. Exp., pt. L\x. p. 6). 



2 Zool. Chall. Exp., pt. xxxi. p. 81. 



3 Narr. Chall. Exp., vol. i. p. 643. 



