STUDIES IN SPICULK FORMATION, 533 
Studies in Spicule Formation. 
IV.—The Scleroblastic Development of the Spicules in Cucuma- 
riide; with a Note relating to the Plate-and-Anchor 
Spicules of Synapta Inherens. 
By 
W. Woodland, 
University College, London, 
With Plates‘32,°33 and 34. 
INTRODUCTORY. 
The early stages in the form-development of the perforated- 
plate and stool spicules of Cucumariide and other holo- 
thurians have been described and figured by many previous 
observers, as e.g. by Théel (10) in 1882, by Hérouard (4) in 
1890, by Mortenson (7) and Kishinouye (5) in 1894, by Gerould 
(2) in 1896, and others, but in no case has the morphogenesis of 
the spicule been systematically studied in relation to the dis- 
position of the scleroblasts or cells concerned in the deposition 
of the spicule. It is true that Hérouard (4) has provided a 
very detailed account of this very subject—as to the manner 
in which the direction of growth of the holothurian plate 
spicule is due to the number and disposition of the formative 
cells,—but since he does not provide any figures in confirma- 
tion of his statements, and since my own observations tell a 
very different tale, I see no reason to qualify the assertion I 
have just made. 
voL. 49, paRT 4,—NEW SERIES. 40 
