ANATOMY OF ASTERIAS. 



179 



placed around the mouth (s), by means of a dilated vertical tube of 

 communication (/), which, from its muscular appearance and great 

 irritability, Tiedemann regards as being equivalent in function to a 

 heart. The circle around the mouth (s) would seem to be arterial in 

 its character, and branches are derived from it which supply the various 

 viscera of the body. 



(470.) But, besides the vessels above described, apparently so dis- 

 posed as to collect and distribute the nutrient fluids, there is another set 

 of canals appropriated to the supply of the numerous vesicles connected 

 with the locomotive suckers ( 456) ; these Tiedemann regards as being 

 totally unconnected with the vascular system properly so called, and 

 considers the fluid contained in them as quite of a different nature. 

 Delle Chiaje, on the contrary, asserts that the two sets of vessels are 

 derived from each other, and describes a peculiar apparatus connected 

 with them as performing an important part in effecting the protrusion 

 of the suckers. 



(471.) The circular Fig. 90. 



vessel around the 

 mouth, which forms the 

 central receptacle of the 

 vascular system, resem- 

 bles a sinus analogous 

 to those of the dura 

 mater in man, and is 

 lodged in a groove be- 

 tween the oral circle of 

 vertebrae and the pieces 

 of the skeleton articu- 

 lated therewith. Con- 

 nected with the sinus 

 above mentioned, and 

 placed regularly in the 

 interspaces between the 

 rays, are several oval 

 vesicles (fig. 90, & 7c), 

 filled with a reddish- 

 coloured transparent 

 fluid. These vesicles, 

 which in Asterias au- 

 rantiaca are seventeen 

 in number, 



Asterias auranfiaca opened from above : a, dorsal parietes 

 reflected ; ft, c, d, floor of the rays, exhibiting the ambulacral 

 vesicles ; e, dorsal circular vessel ; /, heart ; s, circular vessel 

 surrounding the mouth ; fck, ampullae Polianse. 



communi- 

 cate by distinct ducts with the central sinus, and are regarded by Delle 

 Chiaje as reservoirs wherein the nutritive fluids accumulate until 

 expelled by the contraction of the vesicles. Besides the arteries above 

 described as arising from the vascular circle around the mouth, accord- 



