STUDIES IN SPICULE FORMATION. 305 
Studies in Spicule Formation. 
III—On the Mode of Formation of the Spicular Skeleton in 
the Pluteus of Echinus esculentus. 
By 
W. Woodland, 
University College, London, 
With Plates 18 and 19. 
INTRODUCTORY. 
THoucH the mode of development of the skeleton of the 
Pluteus larva has already been ascertained, as regards the 
main features, in the case of several genera, as, e.g., in 
Kehinus (miliaris) by Selenka (17) in 1879, and Théel (28) 
in 1902, in Arbacia (Hchinoid) by Garman and Colton (6) 
in 1882,in Ophiopholis (Ophiuroid) and Echinarachnius 
(Echinoid) by Fewkes (5) in 1886, and especially in Echino- 
cyamus (HKchinoid) by Théel (21) in 1892, yet since this sub- 
ject has not hitherto been investigated in detail in any one | 
instance (excepting the case of Echinocyamus), it is well 
that the following description of the process of spicule forma- 
tion as it occurs in the larva of Echinus esculentus should 
be published. This is further desirable in that I have both 
several new facts of importance to add to our existing know- 
ledge of this process and a few minor suggestions to make 
relevant to the factors concerned. 
The material on which I worked was procured during my 
