226 Transactions of the ["^IimZT-^T 



network, like the concentric Layers of Exogenous stems, at certain 

 regular periods, but also to have the power possessed by the mantle 

 of Mollusca of furnishing an extraordinary supply of the requisite 

 materials when they are required for the reparation of an injury. 



Not very long afterwards, my friend Mr. John Quekett showed 

 me a specimen of Echinus trigonarius in the Museum of the Koyal 

 College of Surgeons, which had sustained an extraordinary mutila- 

 tion ; a large proportion of its spines having been broken or cut across, 

 apparently by the bite of some strong-toothed fish, such as a Scarus 

 or Scarus, of which the stumps that remained also bore marks, as 

 shown in Plate XLIX., Fig. 1. Many of these spines had the conical 

 termination here represented ; and I was at once impressed with the 

 conviction that this termination was a new growth, produced by the 

 reparative power inherent in the organic substance of the spine. 

 This conclusion became a certainty when a longitudinal section was 

 made of one of these conical-tipped spines (Fig. 2) ; for it then be- 

 came obvious that the regular pillared structure v;as terminated at 

 the base of the cone by an abrupt line of demarcation, and that the 

 substance of the cone was formed of that simple or non-differen- 

 tiated calcareous reticulation, which, as I showed in my ' Eeport/ 

 constitutes the elementary type of the skeleton of Echinodermata 

 generally — a generalization which all subsequent observations on 

 its character have tended to confirm.* It further appeared from 

 this section that the new growth proceeds mainly, if not exclusively, 

 from the outer layers of the spine ; a distinct continuity of struc- 

 ture being there traceable, whilst there is a complete interruption 

 between the calcareous reticulation of the central part of the base 

 of the cone and that of the truncated end of the spine on which it 

 rests. 



An account of these spines, with some details of the structure 

 of their new growths, was given by Mr. Quekett, in his ' Histo- 

 logical Catalogue of the Museum of the Eoyal College of Surgeons ;' f 

 and this was repeated in his ' Lectures on Histology,' J with a 

 notice of two spines that had subsequently come into his possession, 

 one of which showed a new growth 1^ inch long, so nearly replacing 

 the part that had been lost as to restore the general form and pro- 

 portions of the spine ; whilst in the other there was seen on vertical 

 section the evidence of four successive reparations. Though his 

 sketch (Fig. 123 b) of this last specimen plainly indicates that these 

 reparations were effected by ingrowth from the superficial layers, he 

 does not notice the circumstance ; but remarks (p. 228) that he has 

 not been able to find, by treating with acid spines that have never 



* See Chap. xii. of my 'Microscope and its Revelations;' Mr. James Salter's 

 Memoir "On the Structure and Growth of the Tootli of Echinus," in 'Philos. 

 Transact.' for 1861; and my own Memoir " On the Structure, Physiology, and 

 Development oi' Atitedon rosaceus" in 'Philos. Transact.,' 1866. 



t Vol. i., p. 304, plate xv., fig. IS. % Vol. ii., pp. 229-231, 



