216 



CCELENTERATA. 



hyaline marginal membrane, which, derived frc^n a prolongation of 

 the hyaline plasma, projects as a hollow cylinder resembling the 

 protoplasmic collar of certain Flagellata* (Cylicomastiyes). [This 



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

 inside the cell. 5, Amphidisc of a gemmule of Spongilla. c, Anchor from Ancorina. d, 

 Hook from Esperia. c, Star from Chondrilla. f, Anchor froTnJSuplcctella asperglllum. g, Ji t 

 needle rays from the same, i, 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 amosboid cells are embedded, 

 and may be regarded, like the gelatinous 

 substance of the Acalepha, as mesoderm, 

 while the external, clearly defined, flat epi- 

 thelium (also in the Asconia, Leucosolenia) 

 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 

 Flaqdlata, and regarded them as great colonies of the latter. 



FIG. 161. Portion of the exter- 

 nal layer of Spongilla with the 

 pores, P (after Luberkiihn). 



