STUDIES IN SPICULE FORMATION. 31 



Studies in Spicule Formation. 



V. — The Scleroblastic Development of the Spicules in Ophiu- 

 roidea and Echinoidea, and in the Genera Antedon and 

 Synapta. 



By 



W. Woodland, 



Deiiioustrator of Zoology, King's College, London. 



With Plates 3 and 4. 



Introductory. 



The greater part of the material utilised in this inquiry- 

 was obtained from the Marine Biological Laboratory at 

 Plymouth, and consisted of two common examples of the 

 Ophiuroidea, viz. the small Amphiura elegans (Amphi- 

 nridfe) and the much larger Ophiothrix fragilis (Ophio- 

 thricidas), and one of the Echiuoidea — Echinus esculentus. 

 Recently-metamorphosed specimens of this latter were mostly 

 obtained from the artificially-reared plutei referred to in 

 Study III (13), and were about a score in number; however, 

 one or two slightly larger specimens were also secured from 

 dredgings. Most of my results have been obtained from 

 observations on the viviparous Amphiura elegans. In 

 this Ophiurid the bursse, as is well known, function as brood- 

 chambers, and, in consequence, young animals are very easy 

 to obtain in every stage of development. The methods of 

 preparation adopted were as follows : — A hundred or more 



