ACALEPH^. 



103 



generation. They may acquire dimensions of many feet diameter, 



and weigh occasionally from fifty to sixty pounds ; and their system 



of nutrition escapes us. They execute the most rapid and continued 



motions ; and the details of their muscular system are unknown. 



Their secretions seem to be extremely abundant; but we 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 general and obvious charac- 

 ters of the AcalephcB are strikingly exemplified, and the observers^ 

 labouring under the disabilities and inconveniences of shipboard life, 

 may be excused if they failed to solve problems of such unusual 

 difficulty. 



With respect to the organs of nutrition of the Medusae, let us see 



what Hunter was able to de- 

 monstrate, and leave for our 

 instruction. In these speci- 

 mens f, which belong to the 

 genus Rhizostoma, he has in- 

 serted his skilful injecting ap- 

 paratus into the stomach {Jig. 

 52, «), plunged, so to speak, " in 

 medias res," and made conspi- 

 cuous by his coloured injection, 

 both the extraordinary route by 

 which the nutriment reaches the 

 digestive cavity, and also the 

 channels by which the digested 

 aliment is distributed for the 

 support of the general system. 



52 



Rhizostoma. 



* Annales du Museum, torn. xiv. p. 219. 

 t Nos. 847. 982, 983. 



H 4 



