996 Mr Thompson on the Star-Fish of 



It is no uncommon thing, in the inferior classes of the animal 

 kingdom, to find animals permanently attached from the period 

 of their birth, and during the whole time of their existence, fa- 

 miliar examples of which we have in the oyster, anomia, and 

 various other bivalve shell-fish, and in numerous compound ani- 

 mals of the classes Zoophj ta and Infusoria. I have also shewn, 

 in my memoirs on the Cirripedes, examples of animals being free 

 and locomotive in their first stages, and afterwards becoming 

 permanently fixed ; but an animal growing for a period as it were 

 a flower, fixed by its stem, and then dropping from its pedicel 

 and becoming, during the remainder of its life, free and locomo- 

 tive, is not only new, but without any parallel in the whole range 

 of the organized part of the creation. No wonder, then, that 

 any naturalist, on the. first discovery of the young animal in its 

 first or fixed stage of existence, ghould consider it as belonging 

 exclusively to those which are known to be permanently fixed, 

 analogy would permit no other conclusion to be formed, and 

 consequently it could be classed with none other except the cri- 

 noideae, one known genus of which tribe participates with coma- 

 tula in being locomotive in its advanced stage ; so that this cir- 

 cumstance connects all these animals into an inseparable group, 

 with which the present state of our knowledge will not permit 

 us to associate any other of the asteriae. 



When, therefore, I formerly described the young of the co- 

 matula* as a new species of pentacrinus, no person could have 

 suspected so anomalous and unexpected a result, as that it was 

 the young state of this curious star-fish, an animal not only free, 

 but leading the most vagrant life of any of the tribe with which 

 it has hitherto been associated by naturalists, — at one time crawl- 

 ing about amongst submarine plants, at others floating to and 

 fro, adhering to thin fragments by means of its dorsal claspers, 

 or even swimming about after the manner of the medusae. In 

 swimming, the movements of the arms of the comatulae exactly 

 resemble the alternating stroke given by the medusae to the liquid 

 element, and has the same effect, causing the animal to raise it- 

 self from the bottom, and to advance, back foremost, even more 

 rapidly than the medusa. Fig. 7, Plate II, represents a coma- 

 tula, after having delivered its stroke to the water. 



Memoir on Pentacrinus europseus. Cork, 1827. 



