the Crinoideae and the Echinodennata. 285 



Before passing from the StelleridtB, it will be well to bear in 

 mind that among their essential characters that of being free 

 locomotive animals must not be lost sight of; also, that their 

 natural position is with the mouth downwards ; that the cavity 

 containing the digestive organs is a pouch-like sac giving off 

 cseca, the refuse of their food in all the Ophiwida, and in many 

 true Star-fishes, being rejected by the mouth; likevvise, that they 

 possess distinct, well-defined oviducts, and are supposed by many 

 naturalists to possess the power of self-impregnation. 



In connecting the Star-fishes with the Crinoideee it will be well 

 to notice two genera, one now extinct, and the other an inhabitant 

 of the seas of oui* own times. These in a very decided manner 

 unite the more ancient Crinoids with the recent Echinoderms. 



First the Marsnpite, whose body, that is, the dorsal portion 

 of it, is covered by sixteen pentagonal plates. Fifteen of these 

 plates are arranged in three tiers or series of five each ; the upper 

 row, being the ray-bearing plates, has in each piece a horseshoe- 

 shaped concavity in its centre for the insertion of the rays, while 

 the lower series rest on the dorso-central pentagonal plate. 



The Marsupite has only been discovered in a fossil state in the 

 chalk beds of Sussex, and has no doubt been long extinct ; and 

 consequently although it furnishes ns with but few indications 

 of its habits and mode of life, yet it directs our attention to a 

 genus which is found in a living state in our owti seas, and which 

 may be considered as the representative of the extinct Marsupite, 

 namely the Comatula, which at once leads us back again to the 

 Crinoids. 



The Comatula in its mature state is an unattached animal 

 ha\ing a depressed orbicular body covered with calcareous plates 

 which inclose the digestive organs. The mouth is centrical and 

 somewhat protrusive, and is surrounded by tentaculated jointed 

 rays or arms. On the dorsal side of the body below the rays 

 are several claspers terminating in a hooked point. These bear 

 a striking analogy to the auxiliary side-arms so common to many 

 species of true Crinoids. 



The Comatula possesses both an oral and anal opening. In 

 its early state it is attached to extraneous substances by a flexible 

 column, and when first discovered was described as the Penta- 

 crinus Europaus. 



When examining these two genera, we see in a very remarkable 

 manner the connection between the free swimming and the per- 

 manently attached Asteriadce, or between the Star-fishes and the 

 Crinoids. 



So perfect are all the arrangements in the organised world, 

 and so complete the gi'adations from genera to genera and 

 species to species, that in studying any one class of animals we 



