SEA-CUCUMBERS. 41 
to $600,000. Spines of certain Echini are used as slate-pencils in some 
countries. 
Fic. 40.—Development of sea-cucumber. A, jelly-like animal swimming ; 
a, sea-cucumber forming within. B, later form, showing tentacles 
and feet. 
Specimens for Study.—Living crinoids are not generally’ 
obtainable, but the fossil stems are to be found in various 
localities (see “ Geology”). The stomachs of cod and 
other fishes often yield brittle stars not found near shore. 
The anchors, dumb-bells, etc., of Holothurians can be seen 
by treating the skin to a solution of potash, and should be 
mounted for the microscope. 
Works on Echinoderms for further reference. 
“Challenger Reports ”; ‘“‘ Depths of the Sea,” Sir Wyville Thom- 
son; ‘‘Smithsonian Reports”; Moseley’s “ Notes of a Naturalist” ; 
“Natural History of the Star-Fish,” A. Agassiz, in ‘‘ Memoirs of Mu- 
seum ‘of Comparative Zodlogy” ; “ Echinoderms of New England,” 
A. E. Verrill, in ‘‘ Boston Journal of Natural History,” vol. x; “ In- 
vertebrata of Vineyard Sound,” Verrill ; ‘Seaside Studies in Natural 
History,” Agassiz; “ Homologies of the Pedicellariz,” ‘“ American 
Naturalist,” vol. vii, Agassiz; “ Reports of the United States Com- 
missioner of Fisheries.” 
