^°mi, MayT^s'a '] Royal Microscopical Society. 227 



been dried, any trace of the soft cntieular investment which has 

 been stated by most writers on the anatomy of the Echinodermata to 

 cover not only the surface of the shell but that of the sj)ines. In this 

 remark, as will j^resently more fully appear, I now entirely concur ; 

 my former assumption that the reparation is effected by the investing 

 membrane of the spine having been based, not on my own observa- 

 tions, but on the doctrine then current as to the existence of such 

 a membrane. 



Before the publication of Mr. Quekett's description, I had made 

 sections of several sjDines which I had obtained from diflerent 

 Museums, showing external appearances more or less distinctly 

 indicative of reparation. One of these (Fig. 5), from a specimen of 

 Echinus trigonai'ius, very closely resembles the spine figured by 

 Mr. Quekett, in Fig. 123 a of his 'Lectures on Histology,' The 

 new growth is nearly 2 inches long ; and only differs externally from 

 the basal portion of the spine, in being of rather smaller diameter. 

 The principal part of it is composed of the ordinary calcareous reti- 

 culation, which has obviously grown inwards from the outer layers of 

 the basal portion; but this is covered with layers of the pillared struc- 

 ture, continuous with those of the basal portion, showing that the 

 new growth, as originally formed, has been invested by exogenous 

 layers produced in the ordinary mode. Another sjiine (Fig. 3), which 

 I obtained from a large Acrocladia, has a new growth 1 J inch long ; 

 but this has a pointed shape, very unlike the cylindrical or somewhat 

 club-shaped figure of the ordinary spine. A transparent section of 

 this spine, of which a portion is represented in Fig. 4, enables the 

 derivation of the new growth from the outer layers of the stumj? to 

 be very clearly traced. And the same is the case in another spine, 

 also from on Acrocladia, of which a portion is represented in Fig. 6. 



In my Memoir on Antedon rosaceus * I have stated that the 

 reticular calcareous skeleton of that Criuoid, when a fresh specimen 

 is treated with dilute nitric acid, is found to possess a homogeneous 

 organic basis, apparently of a sarcodic or protoplasmic character ; 

 through which are dispersed little granular glomeruli, that seem to 

 have occupied the open spaces of the reticulation, and are partly 

 composed of oil-molecules. By treating the spines of freshly- 

 captured Echini in a similar manner, I have found them also to 

 possess a similar organic basis-substance ; and it can scarcely be 

 doubted that it is in the portion of it which occupies the interspace- 

 system of the calcareous network, which is continuous throughout 

 the spine, that the formative capacity rt'sides ; that which forms the 

 basis of that network, when once consolidated by calcareous deposit, 

 probably losing its reproductive power. Now in the small and 

 simply constructed spines of the Echinus miliaris and E. Fle- 

 mingii of our own coasts, in which alone I have as yet examined this 

 * 'Pbilos. Transact.' for 1866, p. 703. 



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