The porifera and coelentera . -Z>.. Fig. 96. Spicules of Heteractinellida. A, typical polyactinfi ; B, rosette-like form; C, D, E, nail-like fonns—Cand H in protile, D from below. (After Hinde.) which may further have three or four rays coming oft at right angles, ornearly so, from one surface of the disc. A characteristic modification ofthis type produces nail-like spicules (Fig. 96, C, I>, E), in which there is adisc with six to nine rays projecting horizcjntally, from the centre of whicha stout ray is given oft in a vertical direction. The rays may be equal or 156 SPONGES unequal
The porifera and coelentera . -Z>.. Fig. 96. Spicules of Heteractinellida. A, typical polyactinfi ; B, rosette-like form; C, D, E, nail-like fonns—Cand H in protile, D from below. (After Hinde.) which may further have three or four rays coming oft at right angles, ornearly so, from one surface of the disc. A characteristic modification ofthis type produces nail-like spicules (Fig. 96, C, I>, E), in which there is adisc with six to nine rays projecting horizcjntally, from the centre of whicha stout ray is given oft in a vertical direction. The rays may be equal or 156 SPONGES unequal in size, and may be straight or tapering, blunt or sharp, smoothor with warts on one surface. Should these obser\ations be coufirmi-d, it is evident that we havehere two groujjs of equal systematic importance with the Hexactinellidsand Demosi)ongiae, which have not left descendants jjersisting to ourtime. In addition, therefore, to the three classes now existing, we shouldhave to add the following :— Class 4. *Octactinellida, Hind
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