NARRATIVE OF THE CRUISE. 



100 



of imbricating plates both on the actinal and coronal areas, a structural feature which in 

 the Palaeozoic Echini was quite common, and which is retained in modern Echini only 

 in the bevel between adjoining plates. Many of the Echinothuridse assume, when 

 fully expanded, a globular outline, and when placed on deck the flexibility of the test 



Fig. 83. — Cystechinwi wyvilii, A. Ag. Seen in profile (denuded) ; natural size. 



gives them peculiar vermiform movements. Their sharp spines, like those of the 

 Diadematidae, inflict serious wounds, and the sting of these huge Echini is very painful. 



Fig. 84.—Phermo»oma luculentum, A. Ag. Seen in profile ; natural size. 



This stinging property is not due to the action of the sharp spines alone, but also in 

 part to the effect of the contents of the baggy envelopes which in a few of the species 

 surround some of the sharp spines. 



