340 EVENINGS AT THE MICEOSCOPE. 



that of a -warty angled cucumber tliat tlie animals I 

 allude to are familiarly called Sea-cucumbers {Holo- 

 thuriadcB). The marine zoologist frequently finds them 

 beneath stones at extreme low water, and larger 

 forms — as big in every direction as a marketable cu- 

 cumber — are occasionally scraped from the bottom of 

 the deep sea by means of that useful instrument, the 

 dredge. If you drop one of them into sea-water you 

 will presently see from one extremity an exquisite array 

 unfold like a beautifully cut flower of many petals, or, 

 rather, a star of ramifying plumes. Soon it begins to 

 climb the walls of your aquarium, and then you catch 

 the first glimpse of its affinity to the Urchins ; for the 

 short warts which run in longitudinal lines down the 

 body, corresponding to the angles, gradually lengthen 

 themselves, and are soon perceived to be sucking-feet, 

 analogous in structure and in function to those with 

 which the Star-fish and Sea-urchin creep along. 



But the relationship becomes more apparent still 

 when we find that the Cucumber has a skeleton of cal- 

 careous substance deposited on exactly the same plan 

 as in the Urchin, viz., around insulated rounded cavi- 

 ties. It is true you may cut open the animal and find 

 nothing at all more solid than the somewhat tough and 

 leathery skia ; but a calcareous skeleton is there not- 

 withstanding, though in truth only a rudimentary one. 

 If we were to cut off a considerable fragment of the skin, 

 and spread it out to dry upon a plate of glass, and 

 then cover it with Canada balsam, we should find — as- 

 sisted by the translucency which is communicated to 

 the tissues by the balsam — that the skin is filled with 

 scattered atoms of the calcareous structure, perfectly 

 agreeing with that with which the solid frame-work of 



