ACANTHASCIN^. 127 



stained. The clioanocyte nuclei appear pale, being not more 

 strongly stained than the reticulum-forming protoplasm. They 

 contain one or more chromatic bodies resembling nucleoli. 

 They can be observed with an unusual degree of distinctness (PI. 

 X., fig. 12) ; this may be due in a measure to their relatively 

 large size, measuring 3| — 4| /^ in diameter (as against le — l/o /-* 

 in Euplectella marshalli). They are thus much larger than either 

 trabecular or archgeocyte nuclei. In optic sections of the cham- 

 ber-wall (PI. X., fig. 14), the clioanocyte nuclei appear oval in 

 shape, as the result of their being fiattened. I believe that I 

 have seen the flagellum in some cases but the collar could never 

 be brought into view with any degree of distinctness. 



C. ACANTHASCIN^e. 



Saccular, moderately thick-walled, often distinctly 

 laterally compressed. Pentactinic hypodermalia gene- 

 rally present; exceptionally wanting. Gastralia, hex- 

 actins; sometimes pentactins, stauractins or diactins. 

 Parenchymalia, exclusively diactins ; never hexactinic. 

 Hexasters consist of oxyhexasters and discohexasters ; 

 the latter being generally in tw^o varieties, the discoct- 

 aster and the microdiscohexaster . The former is in- 

 variably present, but the latter may be wanting; no 

 strobiloplumicome. 



