PLATE X. 



Common Starfish (Asterias Rubens), 

 Linn., 



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



The dorsal integument, with its multitudinous imbedded ossicles, 

 has been removed from the central ray of the trivium, I ; from its 

 left ray ; and from both rays of the anal biviura, a part of it being 

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

 attachment to it of the radial digestive coeca. The digestive and 

 other viscera have been in great part removed from the interior of 

 the two rays of the bivium and the ampullae d 2, and the ambulacra! 

 ossicles k 2 exposed in situ. The digestive coeca 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 inte- 

 gument next to the central disc, have been left undisturbed. 



The Eoman numerals I, II, and III, denote the central and the 

 right and left rays of the trivium, which is distinguishable from 

 the bivium numbered IV and V, by the position of the madreporic 

 tubercle ff and the anus _/, opposite to its central ray I, and to the 

 interradial space between rays IV and V. In the irregularly-shaped 

 Echinodermata, such as the Spatangidae, among the Echinoidea, 

 and Cuvieria, the functions and structure of the bivium and 

 trivium respectively may be very different, and may not only make 

 it easy to demonstrate the existence of a bilateral symmetry, but 

 may also constitute a ventral and dorsal surface respectively. But 



