ANATOMY OF ASTERIAS. 171 



externally with lively tints, and is evidently possessed of considerable 

 irritability, as it readily shrinks under the knife, or upon the applica- 

 tion of various stimuli. When cut into, it has a semicartilaginous 

 hardness ; and fibrous bands, almost resembling tendon in their aspect, 

 may be seen to radiate from the centre of the body towards the extre- 

 mities of the rays. There is no doubt that the movements of the rays 

 are effected by the contractions of this fibrous membrane, and that, 

 especially in the most polyp-like forms, as in Comatula and Gorgono- 

 cephalus, the irritable skin is the principal agent in effecting loco- 

 motion. 



(447.) Besides the calcareous matter deposited in its interior, this 

 outer covering of the Star-fish appears to furnish several secretions of 

 different descriptions. The colouring matter upon its surface is no 

 doubt one of these ; as is a reddish fluid which exudes from the integu- 

 ment of A. rubens, and is of so caustic a quality as occasionally to pro- 

 duce great irritation of the skin in persons by whom individuals of this 

 species are incautiously handled : moreover, in A. aurantiaca the whole 

 animal is coated with a thick mucus, so dense and filamentous that it 

 may be raised in thin films resembling a cobweb, and might easily be 

 taken for a cuticular covering. 



(448.) The exterior of the body is generally rendered rough and un- 

 even by various structures, either imbedded in the substance of the 

 coriaceous skin or projecting from its external surface. We have 

 already described the articulated pieces attached to the rays of Coma- 

 tula and others, which seem to be the most perfectly developed forms 

 of these cutaneous appendages. In the common Star-fish of our own 

 coast, similar spinous processes, but composed of only one calcareous 

 piece, are attached to the inferior margins of each ray, sometimes in 

 several rows ; and, being still moveable, they may be useful in seizing 

 prey, or even as assisting in progression. Upon the dorsal aspect of 

 the body are other calcareous projections, exhibiting a great variety of 

 forms, so as to render the entire surface of the animal uneven and 

 tuberculated. 



(449.) But the most remarkable appendages to the integument of 

 the Asterias are minute bodies, which have been named by authors 

 Pedicellarice, and have been looked upon by many naturalists as distinct 

 animals, allied to Polyps in structure, and living parasitically upon Star- 

 fishes and other Echinodermata. Each of these curious processes con- 

 sists of a short stem, fixed by one extremity to the skin of the Asterias, 

 and terminating at the opposite end in two or three points resembling, 

 in some respects, the prongs of a fork : the stem itself does not seem 

 to be perforated by any canal; nevertheless the terminating points 

 are found to be highly irritable, and quickly seize hold of any minute 

 body placed between them. Some writers regard these bodies as organs 

 of prehension, used under certain circumstances for fixing the animals 



