COMMON STARFISH. 311 



PLATE XI. 



COMMON STARFISH (Asterias rubens), LINN., 



Dissected so as to show its motor, digestive, and reproductive systems. 



THE dorsal integument has been removed from the central ray of the 

 trivium, I ; from its left ray, II ; and from both rays of the bivium, a part 

 of it being left attached to the right ray, V, of the bivium at its apex, to show 

 the attachment of the radial digestive coeca. The digestive and other 

 viscera have been removed in great part from the interior of the two rays 

 of the bivium and the ampullae </2, and the ambulacral ossicles k 2 exposed 

 in situ. The coeca attached to the pyloric portion of the stomach have 

 been displaced from their attachments in the left ray of the trivium ; they 

 have been left undisturbed in the central ray ; and in the right ray all the 

 organs, with the exception of a small part of the dorsal integument next to 

 the central disc, have been left undisturbed. 



I. Central radius of trivium ; a line drawn along the axis of this ray to the 



madreporic tubercle g., would, in the undisturbed condition of the 

 parts, have the anus a little on its left ; and if prolonged, would pass 

 down the interradial space of the bivium (IV and V). 



II. Right radius of trivium, with the greater part of the integument left 



in situ. The inward prolongation or angle of the integument is well 

 seen in the interradial space between arm I and arm II. The dorsal 

 integument contains a large number of ossicula, some of which carry 

 small conical prickly spines, whilst others simply connect the spini- 

 gerous ossicles into a reticulation. Down the centre of each ray the 

 spinigerous tubercles are in this species arranged with considerable 

 regularity, so as to form a mesial series ; in the other portions of the 

 dorsal area, they are scattered irregularly. The intervals between the 

 dorsal ossicula bear respiratory coecal processes of the integument. 



III. Left radius of trivium. The two coeca of the pyloric division of 

 the stomach have been displaced from their normal connections 

 within the cavity of the ray, and are displayed in the interradial 

 space on either side. In the middle line are seen the ambulacral 

 ossicles, and on either side the generative glands, 7*1, 72. 



IV and V. Left and right rays of bivium. The greater part of the repro- 

 ductive organs and the whole of the digestive have been removed ; 

 and the ambulacral ampullae, di, d 2, corresponding to the rows of 



