PEDICELLATA. 391 



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 con- 

 sidered as forming three families. The 



AsTERiAS, Lin., 



Or Starfish, have been so called because their body is divided into 

 rays (generally 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 repro- 

 duce 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 



AsTERiAs, Lam., 

 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 movable spines. The whole 

 surface is also pierced by pores, Avhich allow a passage to tubes much 

 smaller than the feet, that probably serve to absorb water, and con- 

 vey it into the general cavity for a sort of respiration. On the mid- 

 dle of the body, and a little on one side, is a stony plate, with a cor- 

 responding 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 

 creca proceed to each ray, ramifying 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 arti- 

 culated with each 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 movable spines, are observed on the 

 lateral edges of the branches in many species. 



Some of this genus have the figure of a pentagon with rectilinear 



* For details respecting the organization of the Star-fish, Ursini and Holo- 

 thuriee, see the splendid anatomical Monograph of Tiedeinann, Landshut, 1816, 

 in folio. 



