C. Porifera calcaria. 7 



their life history«. — The outer epithelium or so-called »ectodermc^ consists of 

 thin, flattened, plate-like cells, like those described by Schulze for Syc. raphanus. 

 — Bidder has quite another opinion of these cells. »Although this form occurs in 

 the Homocoela, it is in my experience rare. The typical ectoderm (e. g. Ascetta 

 clathrus) I find composed of onion-shaped gland-cells containing a nucleus and 

 granules«. Neither Dendy C-^) nor Bidder believe in Lendenfeld's cilia; the for- 

 mer author suggests that their presence is »merely assumed«, the latter states that 

 the cilia »are completely imaginary«. According to D. the choanocytes are by no 

 means so alike each other as might be supposed by the Statements of other 

 authors. SoUas's membrane occurs certainly in Calcareous sponges. What authors 

 generally say about choanocytes is merely based on the typical forms. A peculiar 

 modification he found in Leucosolenia tripodifera (Crtr.). The flagella were retrac- 

 ted, but the collars in many cases well preserved. Their margins did not come 

 into direct contact, but were united by Sollas's membrane. This membrane, how- 

 ever, instead of having a perfectly smooth surface, showed delicate rod-like 

 processes of uniform length, projecting at right angles from it into the gastral 

 cavity. These processes have a granulär appearance. According to B. this 

 »endoderm« is not only multiform but most proteic. He agrees with Dendy' s 

 description and figures, but believes in the old amoeboid transformation , and 

 recognises complete disappearance instead of mere retraction of the collars and 

 flagella. Dendy (^j found peculiar »endothelial cells« lining the capsules in which 

 lie the larvae; m Leucosolenia wilsoni n. they are thick, plate-like, resembling 

 those described by the author in Stelospongos . The function is to supply the 

 developing embryos with nutriment. Another endothelial cell-form the author 

 found in Leucosolenia stolonifer n. and tripodifera (Crtr.) around the projecting 

 actines of the spicules. It was observed that those actines of the spicules, which 

 project into the cloacal cavity, penetrate the layer of choanocytes and are 

 clothed by a sheath of flattened cells, whereas the choanocytes cease abruptly 

 around the base of the actine. This sheath, however, has nothing to do with the 

 ordinary »Spicula-scheide« of Haeckel. The author is of opinion that these cells 

 are »mesodermal«, carried with the spicules in penetrating between the choano- 

 cytes. »Probably these cells are really calcoblasts, which secrete constant addi- 

 tions of carbonate of lime«. Bidder, on the contrary, is »thoroughly prepared to 

 accept them as endoderm«. — After having shewn how close the relation is be- 

 tween the canal System of a colony and the manner in which the individual »Ascon- 

 tubes« are united together, Dendy (^) distinguishes three sections of Homocoela with 

 regard to the canal System, viz.: — Simplicia, Reticulata and Radiata. The 

 Simplicia include such simple forms as never form colonies and such forms in 

 which the whole colony consists of Ascon-like individuals, which may brauch but 

 never form complex anastomoses nor give off radial tubes. Hence the individu- 

 ality of the members of the colony is always fairly well recognisable. The sim- 

 plest form , which was found amongst the Victorian Sponges , is Leucosolenia lu- 

 casi n. The colony consists of some simple Ascon-tubes united together at their 

 bases. A slight advance in complexity is exhibited by L. stolonifer n., as well in 

 mode of branching as in the canal System. Owing to the comparative thickness 

 of the wall, the pores are no more simple apertures, perforating a thin membrane 

 and »practically identical« with prosopyles. They are rather wide apertures, 

 leading into irregulär canals, which may even brauch, and which finally terminate 

 in the prosopyles. Thus, true inhalant canals are formed, which, in fact, are lined 

 by flat epithelium. In Bidder's judgement this fact is even of generic importance. 

 »Though A. clathrus is much more thickly walled than most of the group , the 

 communication is established by a Single perforated granulär cell as in other 



