144 Descriptions of Preparations. 



is seen the madreporic tubercle ; and a little to the left of a line 

 producing' the long axis of that ray to the centre of the madreporic 

 tubercle^ and near the centre of the disk, is seen the small piece of 

 the apical integument in which the anus opens. From the intes- 

 tiniform portion of the digestive tract immediately following" upon 

 the anus, two diverticula arise, and efflorescing into two or three 

 coecal ampullae, reach a short way into each of the two inter-radial 

 spaces in the disk, which lie on the left of the madreporic or anal 

 inter-radius. In tliis species there are only these two inter-radial 

 coeca; the one nearest the madreporic inter-radius is the larger 

 of the two ; both have their internal surface plicated longitudinally, 

 and from this it maybe seen that, like the 'respiratory trees'' of 

 the Holothuriae, with which they are homologous, they are highly 

 extensible. In a starfish which has died with its stomach pouted 

 out, as it often is during life, these coeca may be observed to be 

 drawn down much farther than the much longer coeca, which are 

 prolonged into the interior of the rays from a lower level in the 

 digestive tract, but are attached to the anti-ambulacral surface by 

 a mesenteric membrane. These latter coeca are seen to take their 

 origin from a much wider portion of the digestive tract as single 

 trunks ; and very shortly after entering the rays they break up into 

 two trees, which, with their foHaceous glandular ampullae, fill up, 

 in this specimen in which the generative glands are in a state of 

 quiescence, the greater part of the interior of the cavity of each 

 ray. At a lower level again than the plane whence the stems 

 of these arborescent coeca take origin, the saccular dilatations of 

 the stomach proper are seen bulging for a short distance into each 

 radial space to the vertebral ossicles in which they are braced by 

 ligaments. The Asteriae are the only Echinodermata in which 

 any radial arrangement attaches to the digestive system beyond 

 that of the calcareous apparatus set around the mouth in all of 

 them, and subservient to the prehension or manducation of food 

 in most except the Crinoidea. In the interior of each ray, and 

 between the ramifications of the digestive coeca, which are here 

 and there slightly divaricated to show them, are to be seen the 

 bilaterally symmetrical biserial rows of ambulacral ampullae on 

 either side of the central stem, resembling that formed by the 

 bodies of a true vertebral column, and made up by the apposition of 

 the mesially articulated ossicles called ' vertebrar from this resem- 



