44 



INVERTEBRATE AXIMALS. 



sponge-colonyj comprised of innumerable horny fibres interlaced 

 into ih continuous network, in such a way as to leave innumerable 

 holes and canals between its bundles. In the living condition, the 



;, 21. — Structure of Spongiila A, Vertical section of the outer layer of Hali- 

 sarca lobiiktris, a Sponj,'e in which the skeleton is wanting, enlarged 75 times 

 (after F. E Schultze) : p p " Pores," or openings of inhalant canals by which water 

 is conducted tn tlie ciliated chambers (ad); e Commencement of a larger exhal- 

 ant canal, conducting from the ciliated chambers to the deeper canals, by which 

 tlie wafer is finally cari'ied off to be expelled from the " oscula" ; g g Young stages 

 uf the reproductive bodies or spores. B, Part of a single ciliated chamber of the 

 same sponge, transversely diviilnd, and enlarged SOO diameters (after ^Saville Kent), 

 showing tlie flagellate ciiUs or " wpnnge-particles," with their inwardly directed 

 flagel'a. C, A single flagellate cell of tlie same, still further enlarged : / Flagellum ; 

 TO Collar round the base of the flagellum; n Nucleus; c Contractile vesicle. 



whole of tnis skeleton is covered externally and internally with 

 a soft protoplasmic material, which has been often tei'med the 

 ''sponge -flesh,'^ as it represents the soft parts of the sponge. 

 Examined microscopically, the *' sponge-flesh" is found to be com- 

 posed of an cnoi"mous number of minute protoplasmic bodies or 



