218 THE ANIMAL KINGDOM. 



1 CHAPTER XIII. 



SPICTJLES OF HOLOTHURI^l. 



are marine animals nearly related to the 

 Star-fish and Echini, belonging to the Radiata, but very 

 unlike them in appearance ; they are outwardly like a simple 

 tough sac, with a plume of delicate feelers or tentacula at 

 its head. It is divided, like the Sea-urchin, into five parts, 

 having five avenues of suckers, and the plume, though 

 more or less plumose, is always a multiple of five. 



They glide about in sunny rock-pools, or lie under stones, 

 and have a curious habit of ejecting all their intestines if 

 irritated or alarmed, yet live a long time perfectly empty, 

 and have the power of reproducing their very complicated 

 internal parts. They possess, though outwardly of such a 

 simple form, heart, liver, intestines, a wondrous system of 

 circulation, and are so prolific that an individual has been 

 known to lay 5000 eggs in one night. 



The spicules we mount for the microscope form a kind 

 of skeleton, being deeply imbedded in the skin, and their 

 form varies with the species. 



SPICULES OF SYNAPTA. 



A species of Holothuria found in the Adriatic Sea ; these 

 -calcareous plates are imbedded in the skin and perforated 

 each with ten or fifteen holes, in one of which an anchor- 

 like spine is fitted with a hinge, by which it is erected or 

 depressed at the will of the animal. 



These are best observed with the blackground illumi- 

 nation. 



SPICULES OF CH1EODOTA. 



Another species inhabiting the Mediterranean, and the 

 plates remarkable for their delicate wheel-like markings. 



