FRESH-WATER SPONGE. 253 



an internal layer of small cells, and a central mass of cells separated inter se by 

 well-formed membranes. 



Spongilla appears to possess a distinct ectoderm, and a mesodermic tissue 

 containing little matrix, but many cells and silicious spicules. "Of the latter, some 

 are scattered as flesh-spicules irregularly in the matrix, others the skeleton spi- 

 cules aggregated by a cementing material into fibres. There appears also to be 

 a system of subdermal spaces. Afferent and efferent water-canals lead to and from 

 ampullae lined by the collared cell characteristic of sponges. 



For the vexed question as to the homology of the tissues here termed ecto- 

 derm, endoderm, and mesodermic tissue, with the parts so termed in other 

 Metazoa, see a paper by Marshall, Ontogenie von Reniera filigrana, Z. W. Z. xxxvii. 

 1882. He appears to prove that afferent and efferent canals are alike lined by 

 endoderm. Schulze, on the other hand (Die Plakinidae, Z. W. Z. xxxiv. 1880, 

 pp. 416 and 436), appears to find that a part at least of the afferent canals are 

 formed by invaginated ectoderm. Ganin's observations on the development of 

 Spongilla show that in that organism the afferent and efferent canals with ampullae 

 are lined by endoderm, but the subdermal spaces (= Leibeshohle) are lined by an 

 epithelium derived from neither ecto- nor endo-derm. Gotte has recently published 

 an account of observations quite at variance with Ganin's, and hard to reconcile 

 with facts observed in the development of other sponges. Cf. Z. A. vii. 1884 

 (A. N. H. (5) xv. 1885); Z. A. viii. 1885. 



Porifera, Vosmaer, Bronn's Klass. und Ordnungen des Thierreichs, ii. (in 

 progress). A monograph of Australian Sponges, von Lendenfeld, Proc. Linnean 

 Soc. of New South Wales, ix. 1884. 



Spongilla and its fresh-water allies. The following references are for con- 

 venience given to one work, where the titles of the originals will be found. Carter, 

 A. N. H. (5) : gemmule of Carterella, vii. 1881 ; ix. 1882 ; fossil spicules, x. 1882 ; 

 xii. 1883. Notes, &c., xv. xvi. 1885. Dybowski, ibid., xiv. 1884. Hilgendorf, ibid., 

 xii. 1883. Marshall, ibid., xii. 1883; (gemmule}, xiii. 1884. Potts, ibid., ix. 1882 ; 

 xiii. 1884; xv. 1885; xvii. 1886. Vejdovski, ibid., xiii. 1884; xv. 1885. 



Retzer, Deutschen Siisswasserschwamme, Inaug. diss., Tubingen, 1883. 



Reproduction of Spongilla. Marshall, SB. Natf. Gesellsch., Leipzig, 1884, 

 (Journal .Roy. Micr. Soc. v. 1885, p. ion); Ganin, Z. A. i. 1878; Gotte, Z. A. 

 vii. 1884 (A. N. H. (5) xv. 1885); Id. Z. A. viii. 1885; Id. Abhandl. Entwick.- 

 geschichte der Thiere, iii. Leipzig, 1886. 



Chlorophyl corpuscles and amyloid deposits. Ray Lankester, Q. J. M. xxii. 1882. 

 Chromatology. Sorby, Q. J. M. xv. 1875. 



Euspongia, Schulze, Die Spongiden, Z. W. Z* xxxii. 1879. 



Growth of spongin fibres, Von Lendenfeld, Z. W. Z. xxxviii. 1883, pp. 265, 

 285, PL xiii. Figs. 25-32. 



Colouring matter of Sponges. Krukenberg, Vergleich. Physiol. Vortrage, ii. 

 1882, p. 51. Digestion in Sponges. Id., op. cit. iii. 1884, p. 125. Von Lendenfeld, 

 Proc. Lin. Soc. N. S. W. ix. 1884, p. 434. Vital phenomena of Sponges, Solger, 

 Biol. Centralblatt, *iii. 1883-84. 



Coelenterate nature of Sponges. Marshall, A. N. H. (5) xvi. 1885 (transl.). 

 Relation to Choano-flagellata. Schulze, A. N. H. (5) xv. 1885 (transl.). 



