ACALEPH^. 



105 



We must suppose the mouths of these excretory vessels to be 

 endowed with an irritability of a different kind from that of the 

 nutrient canals, like the mouths of the different cavities of a ruminat- 

 ing stomach. For, as the orifices of the third and fourth stomacRs 



contract upon the coarse 

 unmasticated food, whilst 

 those of the first and se- 

 cond open to receive it, 

 and close when it is pre- 

 sented to them in its re- 

 masticated state, so the 

 nutrient diverticula of the 

 stomach of the Cyantea re- 

 ceive the digested and ex- 

 clude the excrementitious 

 part of the food, which 

 passes along the anal ca- 

 nals, and is thus rejected 

 from the system. But, it 

 Cyanzea. may askcd, why the Cy- 



ansea should have intestines and vents, whilst the Rhizostoma has 

 neither ? The difference, doubtless, relates to the different organis- 

 ation of their mouths. In the Rhizostoma, only finely comminuted 

 matter, as animalcules and fluids, can obtain access to the digestive 

 sac ; no solid excrements are formed, or require to be expelled ; but 

 the Cyansea with its single and larger mouth can swallow Crustacea 

 and small fishes. 



The discovery of the precise condition of the nutrient apparatus 

 in the Cyancea aurita is due to the ingenuity and perseverance of 

 Prof. Ehrenberg, who induced the living animals to swallow indigo 

 with their food. He has represented the canals so injected, in the 

 elaborate plates of his memoir on the anatomy of this species.* 

 Prof. Wagner f saw the currents of the nutrient fluid in the vascular 

 system of the Oceania : they were produced, not by contraction of 

 the canals, but by the vibration of the cilia lining them. 



The Medusae swim by the contractions of the margin of their 

 gelatinous disc ; and Mr. Hunter has put up a corrugated portion of 

 the disc J, which he seems to have considered as indicative of the ar- 

 rangement of muscular fibres of the part. Prof. Wagner states that 

 the muscular fibres which he detected in Oceania and Pelagia, had 



* Abhandl. der Konigl. Akad. der Wissen zii Berlin, 1 835. 

 ■}- Ueber den Bau der Pelagia noctiluca, fol. 181). 

 \ No. 55. 



