216 



CCELENTEBATA. 



hyaline marginal membrane, which, derived from a prolongation of 

 the hyaline plasma, projects as a hollow cylinder resembling the 

 protoplasmic collar of certain Flagettata* (Gylicomastiges). [This 



FIG. 160. Silex bodies from different silicious Sponges, a, Silex needle from Spongillu, 

 inside the cell. I, Amphidisc of a gemmule of Spongilla. c, Anchor from Ancorina. d, 

 Hook from Esperia. e, Star from Chondrilla. f, Anchor from EuplecMla aspergillnm. g, h, 

 needle rays from the same. /, Six-rayed needle from the same, with central canal. 



structure is commonly known as the collar, and the cells as the 



collared cells.] 



The thick layer in which the skeletal 

 spicules are produced consists of a hyaline 

 matrix, in which irregularly branched or 

 spindle-shaped amoeboid cells are embedded, 

 and may be regarded, like the gelatinous 

 svibstance of the Acalepha, as mesoderm, 

 while the external, clearly defined, flat epi- 

 thelium (also in the Asconia, Leucosolenici) 

 is to be considered as ectoderm. 



The pores or inhalent openings so cha- 

 racteristic of the Sponge body are in 

 reality only intercellular spaces, and are 

 able to close themselves, vanish and be replaced by new pores, 

 which arise by the separation of one cell from another (fig. 161). 



* Upon this ground Clark declared the Sponges to be nearly allied to the 

 , and regarded them as great colonies of the latter. 



FIG. 101. Portion of the exter- 

 nal layer of Sjiongilla with the 

 pores, P (after Luberkuhn) . 



