PEDICELLATA. 469 



those whose olive-like spines are oflen found petrified in chalk, and other 

 ancient formations, called pierresjudaiques. 



The most common species, and particularly those of the coast of France, are 

 merely furnished with slender spines, articulated on small tubercles that are 

 much the most numerous. 9. 



The neighbouring species are distinguished with difficulty, by the greater 

 or less approximation of the bands of holes, the equality or inequality of the 

 tubercles, &c. 



HOLOTHUBIA, Linnceus. 



The Holothurite have an oblong coriaceous body open at each end. At the 

 anterior extremity is the mouth, surrounded with complicated tentacula sus- 

 ceptible of being entirely retracted. At the opposite end is the aperture of a 

 cloaca in which the rectum and organ of respiration terminate, the latter in the 

 form of an extremely ramified hollow tree, which is filled with water, or 

 emptied, at the will of the animal. The mouth is edentate, or merely fur- 

 nished with a circle of bony pieces ; it receives saliva from certain sac-like 

 appendages. The intestine is very long, variously flexed, and attached to the 

 sides of the body by a mesentery ; there is a sort of partial circulation in an 

 extremely complex and double system of vessels, entirely restricted to the 

 intestinal 'canal, and in a portion of the meshes with which one of the two 

 arborescent organs abovementioned is intertwined. There also appears to be 

 a very attenuated nervous cord round the oesophagus. The ovary is composed 

 of a multitude of blind and partly ramous vessels, all terminating in the mouth 

 by a small common oviduct ; at the period of gestation they become enor- 

 mously distended, and are filled with a red and grumous substance that appears 

 to be the ova. Excessively extensible strings, inserted near the anus, appear 

 to constitute the male organs of generation, and consequently these animals 

 are hermaphrodites. When disturbed, it frequently happens that they contract 

 so violently as to rupture and protrude their intestines. 



The Holothuriae may be divided according to the arrangement of their feet. 



In some, they are all situated in the middle of the under part of the body, 

 that forms a softer disk on which the animal crawls, turning up the two extre- 

 mities, in which are the head and anus, that are narrower than the middle. 

 The anus in particular terminates almost in a point. Their tentacula, when 

 developed, are very large. 



ORDER II. 



APODA. 



OUR second order of the Echinodermata, or the Apoda, comprises but a 

 small number of animals closely related to the Holothuriae, but which want 



