MATERIALS FOR A MONOGRAPH OF THE ASCONS. 521 



an exceedingly long and slender ray is formed, projecting 

 far into the gastral cavity, enveloped in a continuous mass of 

 protoplasm, a true plasmodium which contains four nuclei 

 scattered along the spicule ray (PI. 42, fig. 55). 



In cerebrum (PI. 40, figs. 28 — 30) there are two classes of 

 quadriradiates, distinguished by the characters of their gastral 

 rays. In one class the gastral ray is comparatively short, and 

 beset with spines near the extremity (fig. 29) ; these spicules 

 are very characteristic of the species, and have been noticed 

 by all the authors. The other class of quadriradiates, on the 

 other hand, seems to have been generally overlooked, though 

 it is the more abundant in many individuals; it has the gastral 

 ray long and tapering, often slightly curved at the tip, and 

 without spines (fig. 30). Typical examples of these two classes 

 are distinct enough, but nevertheless they are connected by 

 numerous intermediate forms. Thus in some spicules the 

 gastral rays are spiny like that represented in fig. 28, but 

 have the ray prolonged considerably beyond the spiny region ; 

 in others a long tapering ray like fig. 30 may have minute 

 rudiments of spines upon it. 



In the young spicule the gastral ray is slender, straight, and 

 smooth (fig. 28) . After the ray has attained its full thickness 

 at the base the actinoblast migrates towards the tip, leaving 

 the cylindrical basal portion apparently exposed. The nucleus 

 of the actinoblast does not divide, but in the spiny spicules 

 granules resembling chromatin make their appearance, scattered 

 about in the region of the spines (fig. 29). In the smooth 

 spicules similar granules are present, but instead of being 

 scattered they are collected together at the extreme tip of the 

 spicule ray, the nucleus being at the opposite extremity near 

 the basal limit of the actinoblast (fig. 30). I am unable at 

 present to explain these appearances, which were observed in 

 all the spicules examined, and both figs. 29 and 30 could have 

 been repeated, if necessary, to any extent. The impression 

 given is that granules of chromatin are budded off from the 

 nucleus to superintend, as it were, the centres of secretion 

 which give rise to the spines, though it cannot be said that 



