ORGANS OF DIGESTION. 325 



c.), which terminate below in simple lobed dilatations (A. 

 a. a. a. a.} having their surface marked with numerous 

 depressions which are the orifices of internal canals (A. a. b. 

 c.) leading upwards to the stomach. In the middle and 

 upper parts of these eight branches there are fimbriated 

 membranous extensions (A. /. B. /. k.) the numerous 

 vessels of which also anstomose with the principal ascend- 

 ing trunk of each peduncle. On making a vertical section of 

 this rhizostome through the centre of the disk (113. B.) we 

 observe the internal canals (B. b. c.) commencing from the 

 polypiform orifices of the branches (B. a. a.) receiving all 

 the lateral absorbent or respiratory canals (B. f. /. k. k.} in 

 their course, and uniting above to form one large oesophageal 

 passage (B. ra.) before entering the wide central gastric 

 cavity (B. d.) There are more than twelve open 

 pores, the polypiform orifices of these digestive tubes, 

 perceptible on the lobed trilateral dilated base of each 

 peduncle (A. B. a. a.} and the delicate mucous 

 lining of all these digestive cavities can scarcely be 

 detached from the general cellular tissue of the body which 

 they traverse. Thin membranous partitions (B. /. /.) 

 separate the cavity of the stomach (B. d.) from the four 

 surrounding ovarial sacs (B. e. e.) which open externally 

 by distinct apertures (B. i. i.) and sixteen canals radiate 

 from the periphery of the stomach, dividing and anastomos- 

 ing as they proceed towards the outer margin of the disk 

 (B. h. h). The myriads of minute ramifying canals, anas- 

 tomosing freely with each other, form a continuous compli- 

 cated plexus around the free margin of the mantle, and 

 spread extensively on the coloured lobes (B. h. h.) which 

 bound its periphery, thus forming, as in the pteropods, 

 a respiratory apparatus of the most active organ of locomo- 

 tion. In many of the higher medusa, as in the medusa auri- 

 ta (Fig. 113. C. D.) the mouth is single and opens directly 

 from the centre of the inferior surface of the mantle, into a 

 capacious stomach from which numerous vessels radiate to 

 a circular canal surrounding the margin of the disk. The 

 mouth of the medusa aurita is of a quadrangular form, 

 supported by four curved cartilaginous plates, from which 

 are suspended four lengthened tapering lips or tentacula 

 (C. D. p. p.] as we find on the sides of the mouth in most 



