888 



ECHINODERMA 



neatness of pattern there are no spines that can approach those 

 of Echinometra (fig. 673). The spines of Stomopneustes variolas-is 

 are also remarkable for their beauty. No succession of concentric 

 layers is seen in the spines of the British Echini, probably be- 

 cause (according to the opinion of the late Sir J. G. Daly ell) these 

 spines are cast off and renewed every year, each new formation 

 thus going to make an entire spine, instead of making an addition 

 to that previously existing. Most curious indications are some- 

 times afforded by sections of Echinus-spines of an extraordinary 

 power of reparation inherent in these bodies. For irregularities 

 are often seen in the transverse sections which can be accounted 

 for in no other way than by supposing the spines to have received 

 an injury when the irregular part was at the exterior, and to 

 have had its loss of substance supplied by the growth of new 





Pi(i. 676. Transverse section of a spine of (innioriilni-in 



which shows that the prickles on the spine are formed, not by the 

 crust only, but also by the inner reticular tissue. (Prom Bell.) 



tissue, over which the subsequent layers have been formed as usual. 

 And sometimes a peculiar ring may be seen upon the surface of a 

 spine, which indicates the place of a complete fracture, all beyond 

 it being a new growth, whose unconformableness to the older or 

 basal portion is clearly shown by a longitudinal section. 1 The spines 

 of Ci<liii-ix present a marked departure from the plan of structure 

 exhibited in Echinus ; for not only are they destitute of concentric 

 layers, but the calcareous network which forms their principal 

 substance is incased in a solid calcareous sheath perforated with 

 tubules, which seems to take the place of the separate pillars of the 

 Kcliini. This is usually found to close in the spine at its tip also ; 



Sec the Author's description of such reparations in the Moiit/ili/ Microscopical 

 <ln>n mil, vol. iii. 1870, p. -2 '2 5. 



