CORBITELLA AND HETEROTELIA. 7 



The spicular center is ordinarily simply annulated, occasionally 

 supplied with cruciately disposed knobs ; ends of rays being 

 rough-surfaced as usual. Occasionally slender tauactins came 

 under observation. The hexactins are of various sizes. The 

 larger ones may be said to be of a medium size and strength. 

 Often one axis is considerably longer than the two others, the 

 elongated axis not seldom forming bundles in association with 

 diactin elements. 



Of common occurrence are similarly rayed pentactins, in 

 which the unpaired ray exceeds all the others in length (about 

 100/* long; thickness near the center 7 P or less). Many, if 

 not all, of these are probably to be looked upon as the gastralia 

 (PL, fig. 4). 



At places dagger-like hexactins of varying sizes are met with 

 in the preparations. Hilt-ray 50-200 /* long, 4-10 /* thick near 

 the center ; guard-rays about as long as, or somewhat longer than, 

 the hilt-ray in the same spicule ; length of blade-ray usually 

 several times that of the hilt-ray. A large spicule of this 

 category may reach 1 mm. in total length. Some at least of 

 such hexactins are undoubtedly the dermal ia. So, for instance, 

 the rather small hexactins (PL, fig. 2) in which the short 

 hilt-ray of about 50 /* length is quite or nearly smooth with 

 rounded termination ; and also the tolerably large ones (PL, fig. 

 1) in which the hilt-ray (about 200/* long, 10/* thick near the 

 central node and gradually tapering outwards to a point) bears 

 in close apposition graphiocomal rhaphides, besides being dis- 

 tinguished from the other rays on account of the more extensive 

 roughness of its surface. The roughness of the dermal hilt-ray 

 is however never very pronounced. 



The larger hexactins of the parenchyme seem to diminish 



