A. General. 2. Histology. 3 



Maas [cf. Bericlit f. 1893 Porif. p 5] points out that the generative cells 

 can be traced as such iu the sponge larva from the earliest stages of cell differen- 

 tiation; he compares this early segregation with the phenomena in Ascaris de- 

 scribed by Boveri. 



Wilson points out that if we consider germ layers a recapitulation of history in 

 embryos developed from ova, we must attribute the same mnemonic power to 

 gemmules which produce similar layered embryos. This does not strengthen 

 Weismann's position as to germ-cells and somatic cells. It is not only probable 

 that Coelenterates and Porifera are derived from a common ancestor in the Par- 

 enchymella, but that the paragastric sc, gastric cavity in Olynthus and the sim- 

 plest Coelenterates is homologous. The blastopore need not represent a primi- 

 tive organ. - - The entoderm and mesoderrn of Sponges are essentially similar in 

 nature, forming the mes entoderm; but we must recognise also that possibly 

 from the mesentoderm of some larvae are formed the afferent canals, which we 

 know to be phylogenetically derived from the ectoderm. - - Anatomical reasoning 

 would lead us in Esperella fibrexilis to regard afferent and efferent systems as 

 homologous in both apertures and canals ; in Tedania Brucci occur openings larger 

 than pores, smaller than oscula, which may therefore be classified as structures 

 intermediate between the two [afferent or efferent?]. 



Topsent( 1 ) finds that of late too much importance has been attached to the 

 microscleres, as opposed to the rnegascleres in classification. - - Resemblances 

 between larvae are of great classificatory importance. 



Topsent( 3 ) determines 6 new species (Raspailia and Hircinia] by external con- 

 tour; employing le mot espece plutot comme synonyme de forme. 



Vosmaei*( 2 ) finds most species (e. g. Thenea schmidtn, grayi, ivyvitti, delicata, 

 wrighti, intermedia, etc.) to be mere varieties. 



Topsent ( G ) finds that the relative dimensions of spicules vary not only with 

 the size of the individual, but with the age of its different parts; the most robust 

 spicules being generally in the oldest parts of the largest sponges. 



Topsent( 7 ) divides Porifera into Subclasses: (1) Calcarea, (2) Triaxonia, 

 (3) Demospongiae. Subclass. (3) contains orders : (a) Tetractinellida, Mar- 

 shall, (b) Carnosa, Carter [but see infra p 11 Topsent I 1 )], (c) Monaxonida, 

 R. &D., (d) Monoceratina, Ldfd. Tetractinellida are the highest of all 

 Sponges in organisation. 



Lendenfeld( 6 ) for Subclass (3) adheres to the name Tetraxonia [cf. Bericht 

 f. 1889 Porif. p 4] with orders: - (a) Tetraxonida ---- Tetractiuellida, Mar- 

 shall; and (b) Monaxonida, - (b-f-c + d) of Topsent. - The Tetractinellida 

 [= Choristida, Sollas] have given rise to the Lithistida, and polyphyletically to 

 the Monaxonida; Tetranthella [see infra p 10 Lendenfeld etc.] and Tricentrwrn 

 may show the line of passage between Tetraxonida and Axiuellidae. 



Dendy considers Pharetrones may have been descended from normal Hetero- 

 coela. 



Hanitsch (*) gives a glossary to Bowerbank's nomenclature, exhibiting a mo- 

 dern generic name for each sponge illustrated in vols. 3 and 4 of the Monograph; 

 and a classification, with definitions, compiled from the most recent authorities. 



- Topsent ( 5 ) reviews in detail the equivalents given by Hanitsch, and gives a 

 synonymy for all the species figured in Bowerbank's Monograph, vols. 3 and 4. 



2. Histology. 



Topsent( 7 ) recognises in the choauosome of Tetractiuellida : - -(1) Piuaco- 

 cytes, sometimes fusiform to fulfil better their contractile function; (2) Choa- 



Zool. Jahresberielit. 1894. Porifera, C 



