Relationships of the Porifera. 259 



In the second place, from the primitive form have been 

 developed the Siliceous Sponges, and certainly forms with tri- 

 axonid spicules. From these arose first the fossil and recent 

 HyalosponcjicE^ then, by the disappearance of the proper 

 triaxonid spicules and the formation of tetraxonid spicules, 

 the Telraoconina. The stock wliich gave off the lateral 

 branch Hyalospongice produced later on the branches Lithistina, 

 GeodidcBj and Ancorinidce. From the Ancorinidce arose the 

 Flahinidce and Corticidce, and doubtless also the Chondrosidce 

 and Halisarcidce. One portion, however, gave off the branch 

 Teiliyadce^ then the Polymastidce and 8uberitidce^ while the 

 main stem, always degenerating, ran out into the Halichon- 

 dridce. The newly acquired spongin developed more and 

 more and made the spicules superfluous j thus arose progres- 

 sively the Spongidce^ Aplysinidm, and Darwinellidoi. 



As already said, I wish to make no definite assertions con- 

 cerning the main stem, but only to give a possible picture of 

 the ramification of the most important branches. 



There has also been much dispute about the question of 

 the germinal layers. Schulze, after several vacillations, has 

 finally expressed himself very decidedly : — " In addition to 

 the collared cells of the flagellated chambers the whole of the 

 single-layered and continuous epithelium, composed of pave- 

 ment-cells, lining all the cavities, passages, and canals of the 

 exhalant system, from the exhalant opennigs of the flagellated 

 chambers to the margin of the oscular opening, is formed from 

 the endoderm " *. On the other hand, " the layer of flattened 

 epithelium which clothes the outer surface of the sponge and 

 all the inhalant fissures and canals, from the free surface to 

 the inhalant pores of tlie flagellated chambers, is formed from 

 the ectoderm " "f. The remainder of the body is derived from 

 the mesoderm. Schulze certainly seems to wish to extend 

 these remarks, in the first instance applied to Plakina, to the 

 entire group of Sponges. According to Marshall \ the larva 

 (of Reniera Jiligrana) consists of an " ektoderm " and " coeno- 

 blast," which later on divides into "entoderm" and "meso- 

 derm." From this " entoderm " arises the entire canal-system, 

 while the " ektoderm " furnishes only the epithelium which 

 clothes the outside of the body. The third very different view- 

 is that of Goette. According to him § the larval ectoderm 

 vanishes, and consequently the entire sponge is formed from 

 endoderm. 



* Zeitschr. fiir wiss. Zool. Bd. xxxiv. 1880, p. 438. f Loc. cit. 



X Zeitschr. fiir wiss. Zool. Bd. xxxvii. 1882, pp. 221-24rt!. 

 § ' Abhandlungen zur Eutmckehiugsgescliiciite dor Thiere,' iii. Unter- 

 suchungen zur Entwickelungsgeschiciite vou Spongilla flumatilis. 



