\ 2 Porifera. 



spicuies form at least two layers*. The choanocytes are arranged in a stratified 

 epithelium, of which the uppermost only bear flagella. Thus Haeckel's Ascetta 

 labyrinthus, according to Minchin's views, is the ordinary expanded condition of 

 L. clathrus , but with closed oscula; his A. maeandrina is the same a little con- 

 tracted, and A. clathrina is the sponge in an extreme state of contraction. A. mi- 

 rabilis is this sponge partly expanded, partly contracted. L. clathrus therefore 

 is not permanently lipostomous, but is simply so if under unfavourable conditions 

 for life. 



Topsent( 3 ) finds flat ectoderm-cells in Leucosolenia coriacea by means of nitrate 

 of silver. They do not possess flagella, as Lendeufeld stated. In the parenchyme, 

 he finds^two kinds of cells, viz: cellnles granuleuses and cellules sphe'ruleusesc. 

 The former are considered to be of a digestive nature. The latter make the 

 sponge look yellow , green , white, bluish or red suivant la nature des matieres 

 de reserve qu'elles emmagasinent. 



Vosmaer reviews Dendy's paper on the Homocoela [cf. Bericht f. 1891 Pori- 

 fera p 6]. 



