ae W. WOODLAND. 
in position.” This fact explains why it is that the outline of 
the pluteus scleroblast bears such a very different relation to 
the spicule ray compared with that which the actinoblasts of 
calcareous sponges assumes. In Calcarea the actinoblast is 
elongated in the direction of the ray-length, and is in most 
cases cylindrical in form, i.e. envelopes a certain length of 
the ray on all sides; also on one side the cytoplasm forms a 
mound of gradual slope containing the nucleus (text-fig. 8, A). 
In the pluteus larva, on the other hand, the actinoblasts are 
spherical in contour, and are attached to the skeletal rod by 
only a very small portion of the entire circumference, i. e. the 
base of attachment is very limited (text-fig. 8, B). In other 
words, the deposition of lime in Calcarea occurs in the mass of 
the cell-substance, whereas in the pluteus larva it solely occurs 
in the ectoplasm or thin peripheral layer; hence the difference 
of cell-outline in the two cases. As the skeleton of the larva 
Trext-Fic. 8. 
Oras Set 
@ seat 
ich : 
Ses es * 8,78 atteae 
se? MW 
eC, AP ee bh Ox.te 
=, ®.s See Os 
(both in E. esculentus and miliaris, and doubtless all 
other plutei) assumes its adult form, however, the scleroblasts 
become more closely applied to the spicule ray (fig. 29), and 
then resemble the actinoblasts of the Calcarea in form: this 
change in contour being probably correlated with the ex- 
haustion of the cell-substance, the vacuolated cytoplasm 
becoming gradually absorbed and changed in constitution as 
the active deposition of lime proceeds. 
