846 Transactions of the Society. 



XIX. — Notes on the Structural Characters of the Spines of 

 Echinoidea. {Cidaridse.) 



By Professor F. Jeffrey Bell, M.A., Sec. E.M.S. 



{Bead 12th November, 1884.) 

 Plate XIII. 



Notwithstanding the labours of Dr. Carpenter, Mr. Stewart, and 

 Prof. Mackintosh, there still remain points in the structure of the 

 spines of Echinoidea that require much further investigation. 



The first problem to which my attention was directed in a research 

 into the characters of the spines of Cidarids may be stated thus. 

 How do these spines grow, and what is the effect of the enveloping 

 crust, or, as it may conveniently be called, the ostracum, of the 

 spine ? This is, of course, but a branch of the interesting question 

 to which Dr. Carpenter some years ago directed the attention of 

 this Society * when he stated his conviction that the growth of the 

 spine was due to the presence of an " organic basis-substance," and 

 gave up the idea of the possession by the spine of that investing 

 membrane to which, in earlier works, he had ascribed the formative 

 capacity of these organs. This view of the constitution of the 

 Echinid spine is that taken also by Giesbrecht,t whose careful 

 investigation into the minute structure of the teeth of Echinids 

 gives especial value and weight to his opinion; he says, "Das 

 Material, aus welchem der Seeigelzahn, wie auch das ganze Skelett 

 der Echinodermen aufgebaut ist, ist Calciumcarbonat oder vielmehr 

 eine eigenthumliche Mischung desselben mit organischer Substanz." 



If this organic substance penetrates the inner parts of the spine, 

 we may regard the cavities, spaces, and canals which are revealed 



EXPLANATION OF PLATE XIII. 



Fig. 1. — Primary spine of Goniocidaris florigera (natural size), to show the form 

 of the spine, and the prickle-like processes on its surface. 



Fig. 2. — Transverse sections of the same, showing that the prickles are 

 formed not by the crust only, but also by the cancellated tissue. 



Fig. 3. — Transverse section of Phyllacanthus imperialis, especially to show the 

 mode of arrangement of the cancellated tissue. 



Fig. 4. — Transverse section of Stephanocidaris hispinosa, in which, as in figs. 2 

 and 3, the continuation of the canals into the ostracum is distinctly seen. 



Fig. 5. — Transverse section oi Salenia profundi, showing its "acanthostracous" 

 characters. 



Fig. 6. — Section of tip of spine of Echinocidaris spatuligera, to show the mode 

 of distribution of the cap of ostracum. 



The scale to which the figures are drawn is shown on the plate. 



* Monthly Microscopical Journal, iii. (1870) p. 225. 

 t Morphol. Jahrbuch, vi. (1880) p. 79. 



