Chap. III. GENUS PLEUROBRACIIIA. 245 



a large cavity subdivided only by partitions, -without definite circulatory tubes, but 

 along which the fluids are nevertheless circulated up and down and into the 

 tentacles, and discharged either in a retrograde current through the stomach and 

 mouth, or through the tentacles and lateral pores, when such exist. In Discoid 

 Medusae a similar circulation takes place, but without openings either in the peri- 

 phery or opposite the mouth ; here, the fluid accumulated in the digestive cavitj' 

 is circulated through tubes into the periphery and around it, and the refuse matters, 

 retracing their course, are emptied through the mouth. No Medusae have peripheric 

 openings of their chymiferous system through which the refuse matters may be 

 discharged, as Ehrenberg maintains ; but in all of them, as well as in Polypi, the 

 whole digestive apparatus is in direct broad communication with the circulatory 

 apparatus. The fluid circulated is simply chyme mixed Avith water, and carried to 

 all parts through the chymiferous tubes. In Medusas proper this fluid retraces its 

 course, and may be discharged through the mouth. In some Polyps it is also 

 discharged through the mouth only, while in others it may also find an outlet 

 through the tip of the tentacles and through the lateral pores of the spherosome ; 

 but in Ctenophorai it is discharged through the openings of the funnel. These 

 animals never have a continuous alimentary canal with a simple anterior and pos- 

 terior opening, nor a distinct circulatory S3'steni deriving its fluid through lym- 

 phatics from the alimentary cavity ; but all have two closely connected systems 

 broadly communicatmg with one another, through which alimentation takes place, 

 one of which presides chiefly over the function of digestion, while the other circu- 

 lates the whole mass of digested food — that is, ch3^no mixed with water — throughout 

 the system. It is therefore proper, in describing these organs, to avoid any names 

 which may suggest an identity with those of other animals with which they are 

 only analogous. For this reason I have ado^jted the name of coeliac caA'ity for 

 the digestive sac, and called funnel the central chj-miferous cavity ; and its branching 

 tubes, chymiferous tubes or chymiferous vessels. The circulation which takes place 

 in this system of tubes is not to be homologized with a blood cii'culation : it is 

 only a chyme circulation, the fluid moving to and fro in opposite halves of the 

 body by their alternate contractions. 



If we next consider the oblong area, I must first correct a mistake I made 

 in my paper upon Beroid Medusas, in which I stated that the space circumscribed 

 by its outline is a hollow space, extending forward and backward from the two 

 cloacal bulbs, in a direct prolongation of the cavity of the bulbs. I must have 

 been misled by an oblique view of the funnel, producing the appearance of a 

 circulation in the area itself The ridge which circumscribes this area is very 

 definite, and, though smooth, slightly prominent upon the surfiice, so that the circum- 

 scribed area is really a bi'oad, shallow depression, covered with superficial vibratile 



