ACALEPaa:. 



163 



perceive nothing satisfactory as to their origin. They have a kind of 

 very active respiration ; its real seat is a mystery. They seem 

 extremely feeble, but fishes of large size are daily their prey. One 

 would imagine their stomachs incapable of any kind of action on 

 these latter animals : in a few moments they are digested. Many of 

 them contain internally considerable quantities of air ; but whether 

 they imbibe it from the atmosphere, extract it from the ocean, or 

 secrete it from within their bodies, we are equally ignorant. A great 

 number of these Medusae are phosphorescent, and glare amidst the 

 gloom of night like globes of fire ; yet the nature, the principle, and 

 the agents of this wonderful property remain to be discovered. Some 

 sting and inflame the hand that touches them ; but the cause of this 

 power is equally unknown." * 



In this series of lively paradoxes the more obvious characters of 

 the Acalephje are strikingly exemplified ; but I have quoted them 

 rather to contrast with the actual knowledge which has since been 

 gained on these points, and as showing how little the best and most 

 abundant opportunities of observing the Acalephae will avail, if the 

 higher powers of the microscope be not brought in aid of the inves- 

 tigation. Before, however, entering upon these results of later re- 

 searches, let us see what Hunter was able, by the ordinary anatomical 

 procedures, to demonstrate and leave for our instruction. In these 

 specimens!, which belong to the genus Rhizostoma, he has inserted 

 his skilful injecting apparatus into the central cavity of the body 



{fig. 75, a), plunged, so to speak, 

 " in medias res," and made con- 

 spicuous by his coloured injec- 

 tion, both the extraordinaryroute 

 by which the nutriment reaches 

 that cavity, and also the channels 

 by which it is distributed for the 

 support of the general system. 

 The prolongation of the common 

 cavity a into the base of the 

 proboscis (i) there divides into 

 four canals (c), which enter the 

 base of the four branches (/>, p), 

 into which the proboscis divides. 

 These branches again divide and 

 subdivide along their plicated bor. 

 un,xo5toina. ^^^ . ^j^^ nutrient canals follow 



these ramifications, and terminate in numerous fringed pores (</, d), 



♦ CXXXVII. p, 219. f Nos. 847. 982, 983. 



V 2 



