74 ACALEPH.E. 



of the disc, dividing and subdividing into numerous small branches, 

 which anastomose freely with each other, and ultimately form a 

 perfect plexus of vessels as they reach the margin of the mush- 

 room-shaped body of the creature. The radiating vessels are 

 moreover made to communicate together by means of a circular 

 canal (Jig. 29, e) which runs around the entire animal, so that 

 every provision is made for an equable diffusion of the nutritive 

 fluid derived from the stomach through the entire system. Now, 

 if we come physiologically to investigate the nature of this 

 simple apparatus of converging and diverging canals, we cannot 

 but perceive that it unites in itself the functions of the digestive, 

 the circulatory, and the respiratory systems of higher animals : 

 the radiating canals, which convey the nutritive juices from the 

 stomach through the body, correspond in office with the arteries 

 of more perfectly organized classes ; and the minute vascular 

 ramifications in which these terminate, situated near the thin 

 margins of the locomotive disc, as obviously perform the part of 

 respiratory organs, in as much as the fluids which permeate them 

 are continually exposed to the influence of the air contained in the 

 surrounding water, the constant renewal of which is accomplished 

 by the perpetual contractions of the disc itself. 



(1 01.) Before closing our description of the alimentary system of 

 the Pulmonigrade acalephse, we must mention some accessory organs 

 of recent discovery which are in connection with it. Eschscholtz* 

 describes a series of elongated granular bodies, placed in little de- 

 pressions around the margin of the disc, which seem to be of a 

 glandular nature, and apparently communicate by means of minute 

 tubes with the nutritious canals : these he regards as the rudiments 

 of a biliary system. Other observers assign a similar office to a 

 cluster of blind sacculi or caeca, which are connected in some 

 species with the commencement of the radiating tubes ; it is, 

 however, scarcely necessary to observe that such surmises relative 

 to the function of minute parts are but little satisfactory. 



(102.) The Ciliograde acalephse, although their digestive system 

 varies considerably in its general arrangement from what has been 

 described in the Pulmonigrade division, will be found to exemplify 

 in an equally perfect and perhaps more striking manner the for- 

 mation of the vascular and respiratory systems from an extension 

 of the nutritive canals. In the Beroeform species (Jig. 22) the 



* System der Acalephen. Berlin, 1829. Annales des Sciences Nat. vol. xxviii. 

 p. 251. 



