64 ÄHT. 1. 1. IJIMA : HEXACTIXELLIDA, III. 



means about the same as to say that the dermalia are but slightly 

 differentiated from the parenchymalia. Like these they are on 

 the whole large, or moderately large ; quite variable in the 

 number of rays ; and often irregular in shape, not only in having 

 rays of different lengths in the same spicule but also in that 

 these are more or less bent. A large dermalia may show dimen- 

 sions nearly equal to those of the largest parenchymalia. As 

 regards the number of mys, which in character quite agree with 

 those of the parenchymalia, the dermalia are commonly pentactinic, 

 tetractinic or triactinic, and sometimes even hexactinic or diactinic. 

 Hexactinic dermalia are generally so situated that the central 

 node lies a short distance below the dermal surface. Four of the 

 rays, representing two axes, run paratangentially and usually 

 associate, soon after their origin from the central node, with other 

 dermalia to form bundles of varying strength. A fifth ray is 

 directed proximad, while the opposite distal ray is either so short 

 that it never projects beyond the dermal surface or is otherwise 

 so bent as to pursue a paratangential course in the dermal layer. 

 Such hexactinic forms occur only occasionally : they are of interest 

 as occupying a position which may be said to be still j)artly 

 parenchymal. — Pentactinic dermalia usually have the four cruciate 

 rays disposed paratangentially, the fifth unpaired ray dipping 

 inwards into the pillars. Occasionally tlie spicule may be so 

 unnaturally flattened by the bending of its rays that all five are 

 taken up into the dermal layer, the surface of which is thereby 

 made more or less uneven. — When tetractinic, the dermalia are 

 either stauractins or of the form which shows one complete axis 

 and two half-axes. The stauractins generally lie in the plane of 

 the layer with all the four rays. In the case of the other form 

 of tetractins, either one of the unpaired rays may be directed 



