216 



CCELKNTERATA. 



hyaline marginal membrane, \vluch, derived from a prolongation of 

 the hyaline plasma, projects as a hollow cylinder resembling the 

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



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

 inside the cell. J, Amphidisc of a gemmule of SpongiUa. c, Anchor from Ancorina. d, 

 Hook from Egperia. c, Star from Chondrilla. f, \nckorfromEuplectella aspcrgiUum. g, h, 

 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 

 |Q spindle-shaped amoeboid cells are embedded, 

 and may be regarded, like the gelatinous 

 substance of the Acahpha, 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 bod}' 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 (tig. 1G1). 



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

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



FIG. 161. Portion of the exter- 

 nal ln.yrrnt' ,S),,,w V >Y/,i \ v ith the 

 pores, P (after Luburkiihn). 



