210 Objects for the Microscope. 



SPICULES OF ALCYONIUM DIGITATUM. 



These are likewise abundant in that polype so common 

 in some parts of our coast, the caves at Tenby, and the 

 Gouliot Caves in Serk, or are often washed up on the 

 sea-shore after a storm. Fishermen call them dead men's 

 fingers, and they do look like a large yellow finger or 

 thumb, tough and ugly, until, as with the Gorgonia, we 

 replace it in sea-water, when the same kind of beautiful 

 zoophytes appear from the multitude of little spots which 

 stud the surface. These spicules give firmness to the skin, 

 and form a sort of skeleton. 



SECTION OF ECHINUS SPINE. 



This beautiful purple or golden star, with fretwork and 

 circles in many varieties, is a section or very thin slice of 

 one of the spines of the Echinus, Sea-urchin, or Sea-hedge- 

 hog, as it is sometimes called at the sea-side by fishermen 

 and boys, who either dredge them up from the depths of 

 the ocean, on oyster-beds, or find them at low- tide in the 

 crannies of rocks. There are many species ; some very 

 large and bristled over with small spines ; some exceeding 

 small, scarely larger than a marrowfat pea ; others, again, 

 about the size of a hen's egg, with fewer but much 

 longer spines, the Cidaris. The common Echinus has no 

 less than four thousand spines for its defence, the 

 structure of each spine presenting these beautiful varia- 

 tions. The centre is usually occupied by a network, 

 bounded by a row of what appear to be transparent spaces, 

 but are really sections of those strengthening pillars 

 which run up the spine and form the exterior of every 

 layer. Sometimes these sections of Echinus have annular 

 bands, dividing a finely reticulated space, and some have 

 hollow spaces. They should be seen on the dark illumi- 

 nated ground with the dotted lens, or the parabolic 

 illuminator, when the effect is quite magical. Also using 



