148 TEANS4CTI0NS LIVERPOOL BIOLOGICAL SOCIETY. 



tube-foot, and are separated from its cavity by a delicate 

 lining of ill-defined epithelial cells. They are wholly 

 longitudinal in every species examined. On approaching 

 the terminal sucker {Asterias, Solaster) the fibres converge 

 towards its centre, from which point they are distributed 

 in beautifully regular radiating strands to its periphery. 

 External to the muscular layer is (1) a layer of connective 

 tissue ; (2) a layer of nerve fibrils with ganglion cells ; (3) 

 an epithelial layer in which the cells are of considerable 

 length, and consist of supporting cells, sensory cells, and 

 gland cells, the latter occurring largely in the sucker; and 

 (4) the structureless cuticle. It seems to me that con- 

 traction of annular fibres such as Romanes described would 

 result rather in the extension of the tube-foot at the 

 expense of its diameter, for a valvular arrangement 

 prevents the reflux of the contained fluid from the tube- 

 feet into the radial water-vessel. Extension ib, moreover, 

 brought about by the contraction of the ampullae, while 

 the longitudinal disposition of the muscular fibres is quite 

 sufficient to account for all contractile movements. The 

 second statement, with reference to complete retraction of 

 the tube-feet within the body of the animal is entirely 

 without foundation. Even after immersion in the strong- 

 est alcohol the tube-feet are never so retracted. The 

 ectodermal and nerve layers are certainly thrown into 

 numerous annular folds, and it is possible that a super- 

 ficial examination of these led Mr. Bomanes to describe 

 them as annular muscles. 



List of works referred to in the text. 



1. Durham, H. E. — "On Wandering cells in Echino- 

 derms, etc.," Quart. Journ. Micr. Sci., XXXIII, (1891). 



2. Cuenot, L. — " Contributions a FPjtude anatomique 

 des Asterides," 'Theses pres. Fac. d. Sc.,' Paris, 1887. 



