466 EtHINODERMATA. 



extremities, that these animals effect their progressive motions. Vessels 

 proceeding from these feet extend to trunks which correspond to their 

 ranges, and which terminate near the mouth. They form a system distinct 

 from that of the intestinal vessels observed in some species *. 



Linnaeus divided them into three very natural, but numerous genera, and 

 composed of such various species, that they may be considered as forming 

 three families. The 



ASTERIAS, Linnteua, 



Or star-fish, have been so called because their body is divided into rays (gene- 

 rally five), in the centre of which, and underneath, is the mouth, that is also 

 the anus. 



The framework of their body is composed of small osseous pieces, variously 

 combined, the arrangement of which merits examination. Their power of 

 reproduction is very great, as they not only reproduce the rays which have 

 been separately removed, but a single one with the central ray remaining will 

 reproduce all the others ; for this reason their figure is frequently irregular. 

 In the 



ASTKRIAS, Lamarck, 



Or Asterias, properly so called, each ray has a longitudinal groove above, the 

 sides of which are perforated by the little holes before-mentioned, for the 

 transmission of the feet. The rest of the inferior surface is furnished with 

 small and moveable spines. The whole surface is also pierced by pores, which 

 allow a passage to tubes much smaller than the feet, that probably serve to 

 absorb water, and convey it into the general cavity for a sort of respiration. 

 On the middle of the body, and a little on one side, is a stony plate, with a 

 corresponding internal canal, filled with a calcareous matter, which is thought 

 to serve for the growth of the solid parts. Internally, we find a large stomach, 

 immediately on the mouth, from which two caeca proceeds to each ray, rami- 

 fying like trees, and suspended (each) to a sort of mesentery. There are also 

 two ovaries in each ray, and it appears to us that they possess the faculty of 

 self-impregnation. A particular system of vessels is connected with their 

 intestines, and another with their feet. 



M. Tiedemann thinks that their nervous system consists in a very fine thread 

 which surrounds the mouth, and sends a branch to each foot, which runs 

 between those organs exteriorly, and gives off" two twigs internally. 



The osseous framework of each ray consists of a sort of column extending 

 along the inferior surface, and composed of vertebrae articulated with eacli 

 other, from which proceed the cartilaginous branches that support the exterior 

 envelope. Between the roots of these branches are the holes that transmit the 

 feet. Other osseous pieces, frequently furnished with moveable spines, are 

 observed on the lateral edges of the branches in many species. 



For details respecting the organisation of the Star-Fish, Ursini, and Holothurite, see 

 the splendid anatomical Monograph of Tiedemann. Landshut, 1816, in folio. 



