242 Prof. E. Hack el on the Position of the 



( Calcisjjongice) *. The Myxospongia? are characterized by the 

 complete absence of a skeleton, the Fibrospongiee by their 

 partly homy, partly siliceous, fibrous skeleton, and the Calci- 

 spongiaj by their calcareous (not fibrous) skeleton. 



The comparative anatomy and ontogeny of the Sponges 

 allow us to assume with tolerable certainty that all the 

 different forms of this class originate from a single common 

 stock form, ?i primitive sponge [Archispongia) '\ . That all the 

 various Calcispongiaj may be deduced without any difficulty 

 in the most natural manner from a common stock form, 

 Olynthus^ has already been satisfactorily proved ; the ontogeny 

 of the CalcispongiiB leaves no doubt upon this point. Oscar 

 Sclmridt has also shown that the united horny and siliceous 

 sponges (our Fihrospongice) must all have descended from a 

 common stock form, which we will denominate Chalynthus ; and 

 we shall certainly not be far wrong if we assume that the common 

 root of both groups is to be sought in the skeletonless group of 

 the Myxospongiffi ; for, as in all other organisms, so also in 

 the Sponges, the formation of the skeleton is to be regarded 

 phylogenetically as a secondary, and not as a primary act of 

 organization. We should therefore have to derive the Fibro- 

 spongite and Calcispongige from the common stock group of 



* The class of Sponges has hitherto been usually divided, after Grant's 

 ex.ample (1826), in caccordauce with the three different modes of formation 

 of their skeleton, into the three subclasses of the Horny Sponges (Cerato- 

 spongia), Siliceous Spongers (Silicisjwnt/ue), and Calcareous Sponges (Calci- 

 spoiiffice). Oscar Schmidt has shown, however, that the separation of the 

 Horny and Siliceous Sponges is untenable, because the two groups are 

 interwoven with each other most multifariously, and stand in the closest 

 polyphyletic connexion (Algier. Spong. 1808, p. 35). I therefore propose 

 provisionally to unite the two groups in the division of the Fibrous 

 Sponges (Fibrosponf/i<T), because in the dried state both exhibit the 

 characteristic Jibrous te.iiwe, of which both the Calcispongife and the 

 Myxospongise are quite destitute. The establishment of the Gelatinous 

 Sponges (iKi/xospoiu/ice — the best-known representative of which is 

 Halisarca) as a distinct third group seems, upon phylogenetic grounds, 

 unavoidable. 



t The conviction of the monophyletic origin of the whole class of 

 Sponges becomes more and more firmly established the further we 

 penetrate into their study. On the other hand, the assumption of a 

 polyplu/ldic origin, which, on one's first superficial acquaintance with the 

 sponges, seems to possess the most claim to confidence, loses more and 

 more in probability the further we penetrate. Moreover Oscar Schmidt, 

 who of all spongiologists undoubtedly possesses the most comprehensive 

 view of the whole great form-series of this class, and who, by virtue of 

 his clear imderstanding of the theory of descendence, is most justified in 

 pronouncing judgment upon this question, derives all the various groups 

 of sponges from a common stock group, which he denominates Proto- 

 spungice (Atlant. Spong. 1870, p. 83 ; "The Natural System of Sponges," 

 Mittheil. des naturwiss. Voreins fiir Steiermark, Bd. ii. Heft 2, 1870). 



