DIA TOMSECHINODERMA TA. 



141 



were: Bacillaria paradoxa, Nitzschia sigmoidea, N. lanceo- 

 lata, Grammatophora marina, A mphiprora alata, Pinnularia 

 radios a, and P. viridis. 



FIG. 125. 



FIG. 126. 



Books which may be consulted: Rabenhorst's 'Flora 

 Europaea Algarum ' ; J. Smith's ' British Diatomaceae ' ; 

 Donkin's ' British Diatomaceae ' ; and Schmidt's ' Diato- 

 macean Atlas.' 



ECHINODERMATA. The marine objects, star- fishes, sea- 

 eggs, or sea hedgehogs, may always be taken at- low water 

 after a spring tide. In their earlier stages they are ex- 

 tremely interesting, being infusoria-like organisms, and 

 often appearing without any internal structure whatever. 

 They furnish the microscopist with abundance of material. 

 The prickles or spines, hooks, and the pedicellaria make 

 interesting and instructive objects. 



A section of Echinus spine is used as a test for the 

 flatness of field in low-power objectives, while a section of 

 a small spine may be used for the same purpose with higher 



