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



Family Spongid^. 



The family of SpongidfB possesses a larger number of genera than any other family 

 among the Keratosa, but it is only in Aplysinidae that we meet with genera of such con- 

 ditional characters. 



Euspongia, Hijypospongia, Caxiosiwngia, Stelospongos. 



The genus Euspongia has its own history. Established in the year 1859 by Bronn, 

 it has been adopted by 0. Schmidt, although not immediately. It was not adopted by 

 Alpheus Hyatt, who returned to the old name of Spongia, auctorum, but has been again 

 recalled by F. E. Schulze, although with a certain reserve. Prof Schulze, though adopting 

 this name as a generic one, still lays stress upon the fact that the genera Euspongia 

 (which he characterises by fine skeletal fibres forming very small meshes) and Caco- 

 spongia (characterised by him as well as by 0. Schmidt,^ from whom it originates, by 

 comparatively thick skeletal fibres and large meshes) are very closely allied to one 

 another, and that with respect to some intermediate forms the question of whether the 

 classifier has to do with a Cacospongia or Euspongia is to be decided only according 

 to his individual opinion.^ One might say that the matter is not so very complicated ; 

 one would believe that the Cacospongice and Euspongice are divergent branches of the 

 general genealogical tree (in the sense that the skeleton presenting a supporting apparatus 

 for the soft parts, one group of Spongidaj have adopted thick fibres and large meshes, the 

 other fine fibres and small meshes, both kinds of skeleton being thus mechanically 

 perhaps of equal strength), connected by the presence of all possible intermediate stages; 

 that in some thousands of years, when the latter have died out, spongiology wUl have to 

 deal with two very good genera. The matter is, however, by no means so simple, owing 

 to the fact that each of these genera shows other special modifications, and the genus 

 Euspongia, namely, in the direction which leads us to the genus Hipp)ospongia, F. E. 

 Schulze ^ ; a Cacospongia in order to become a Stelospongos, 0. Schmidt.* F. E. Schulze 

 characterises his genus Hippospongia by the presence of a well-developed system of 

 canals permeating the body of the sponge, often in such a manner that between them 

 only comparatively thin partition -walls can be found, and further, by the absence of 

 primary fibres which are directed in Euspongia and Cacospongia perpendicularly to the 

 external surface, the latter character being in causal connection with the peculiarity first 

 mentioned; the genus Stelospongos was established in 1870, and characterised by the 

 differentiation of the skeletal fibres in separated columns du-ected in a more or less 

 regular manner radially from the basis of the sponge towards the external surfaces, 

 and consisting each of a compact network of vertical primary and horizontal 



1 Spong. d. adriat. Meer., p. 26. 2 Zeitschr.f. wiss. ZooL, Bd. xxxii. p. 612. 



3 Zeitschr. f. iviss. ZooL, Bd. xxsii. p. 614. * SpoQg. des atlant. Gebiet, p. 29. 



