184 JULY. 



the Sea-Urchin and the Encrinite, would imagine 

 that they possessed any close natural relationship, or 

 would suspect that they could have been framed on 

 the same model ? Yet it is really so ; there is a common 

 plan of structure in both ; pervading, too, many inter- 

 mediate forms, which at first sight would seem to mani- 

 fest as little resemblance to the one as to the other. 

 It would, in fact, be easy to select from any well- 

 furnished museum a continuous chain of specimens, 

 whose links approach each other so closely as to form 

 an unbroken series from the Urchin to the Feather- 

 star. 



Among the Urchins proper there are some species, 

 such as the Sphere Sea-egg, and the one known as 

 Fleming's, which have a figure not far from that of a 

 globe. Others are much more depressed, of which the 

 little Purple-tipped is a notable example. Still the 

 spherical shape is conspicuous. From this rounded 

 form other species, more and more flattened, gradually 

 lead to the Scutella, which takes the form of a thin 

 round plate, quite flat beneath, but slightly convex on 

 the upper surface. The structure is the same as before, 

 but the spines appear to the naked eye only as very 

 minute hairs ; but, when magnified, are found to be of 

 the most elaborate workmanship, each having a mov- 

 able socket -joint. In the genus Clypeaster, the round 



