530 E. A. MINOHIN. 



rally, as arising each within one single mother-cell. 

 Sometimes even, as in the case of the bundles of hair-like 

 spicules known as trichites, more than one spicule may arise in 

 the scleroblast. In view of this pleasing unanimity with 

 regard to the first origin of the siliceous monaxon spicule, it is 

 to be regretted that so little seems to be known of the fate of 

 the primitive scleroblast. Does the mother-cell persist on the 

 fully formed spicule? Does the nucleus of the secreting cell 

 remain single, or does it ever divide ? These are questions yet 

 to be answered. Carter discusses the point, and is of the 

 opinion that '' ornamental or subsidiary parts, such as the 

 spines, &c., are subsequently added, probably after the spicule 

 has left the mother-cell, and has got into the intercellular 

 sarcode, as shown by the central canal never extending into 

 them" (1875, p. 12). Here, then, we see the belief very cleai'ly 

 expressed that the mother-cell is not responsible for the whole 

 spicule, even in simple forms ; and as no one would now ascribe 

 any skeletogenous function to the jelly or " sarcode " of 

 Carter, it must be supposed that other cells besides the original 

 mother-cell take part in aiding the growth of the spicule. 

 Ridley and Dendy are also of opinion that " it is pretty certain 

 that the larger forms at any rate become free from the parent 

 cell (silicoblast) before attaining their full size" (1887, p.xiv). 

 On the other hand, Maas found in Spongilla larvse spicules of 

 \ mm. in length, with only one silicoblast nucleus, and thinks 

 " that the whole duration of the growth only claims a single 

 cell, the more so as he has never seen spicules with cells 

 applied to them like an epithelium" (1890, p. 539). Delage 

 also (1892) figures many instances of spicules and their cells, 

 but never more than one cell to a spicule. But in the 

 " shovels " (anisochelse) of the Esperia larva Maas found 

 four nuclei to each shovel, one on each side of the blade and 

 one on each side of the shaft (1892, p. 420, PI. xxviii, fig. 19). 

 These shovels are united into rosettes, and this fact suggests, 

 according to Ridley and Dendy, that each such rosette origi- 

 nates within a single cell (1887, p. xx). From all this con- 

 flict of evidence and opinions the only thing clear is that the 



