ACALEPIIJE. 



43 



stance of fishes being found in them.* From 

 each sac, four vessels arise, which run out- 

 wards to the circumference of the animal. 

 Other species (e. g. medusa cup'dtuta) have the 

 four gastric sacs in free communication with 

 one another ; and, frequently, (e. g. in pelagia, 

 (///y.sy/o/v/, and teginu,) in connexion with these, 

 there are four other sacs, lined with a more 

 dense membrane than the former. These gas- 

 tric appendages have the form of simple canals 

 in equorea and tima ; and of branched vessels 

 in medusa and st/ienonia. 



They were chiefly such pulmograda as have 

 their disc bell-shaped that were formerly sup- 

 posed to be ugustric. It was imagined that 

 alimentary matter being received within the 

 campanulate depression, its orifice was con- 

 tracted, and nourishment taken up by im- 

 bibition through the walls of the disc. But 

 an attentive examination of Cari/bdca mar- 

 supialis, (Peron,) one of the animals which was 

 believed to beagastric, has satisfied Dr. Milne 

 Edwards that a mouth and an internal cavity 

 connected with it do really exist. The great 

 transparency of this animal renders the dis- 

 covery of its internal structure a matter of con- 

 siderable difficulty, excepting when coloured 

 injections are used. Dr. Edwards found within 

 the funnel-shaped cavity of Carybdea, and, as 

 it were, pendent from its roof, a projection of 

 very delicate tissues, evidently forming tenta- 

 cula surrounding a central mouth, and a 

 stomach, from which proceed four long canals 

 leading to the tapering filaments which hang 

 down from the margin of the body of the 

 animal. These canals, Dr. Edwards believes 

 to be analogous to the radiating vessels of 

 rhizostoma. There exists just at the com- 

 mencement of each canal, and opening into it, 

 a group of minute cylindrical sacs, which may 

 be regarded as biliary organs .f But in most 

 of the pulmograda these organs are situated on 

 the margin of the disc. Generally, they pre- 

 sent the appearance of glands, being distinctly 

 granular in their structure. They are opaque, 

 have a lengthened form, and are lodged in 

 little depressions, and surrounded by cup- 

 shaped folds of the external integument. They 

 are connected with the gastric appendages by 

 small tubes.}; 



In Aurelia phosphorea, (Lam.) (Pelagia, 

 Esch.) which formed the principal subject of 

 Spallanzani's observations on the acalephae, 

 there are four groups of membranous tubes, 

 convoluted, and resembling in structure the 

 intestines of vertebrate animals. Although he 

 did not trace their connexions, Spallanzani 

 appears to have regarded them as truly parts 

 of the alimentary canal. He observed that 

 they exhibit a peristaltic motion, both in the 

 water and in air, which can be increased by 

 the application of stimuli. 



The food of the pulmograda consists of 

 various marine animals small fishes, mollusks, 



* Gaede, Beytrage zur Anat. und Phys. der 

 Medusen. 



t Ann. dcs Sciences Nat. xxviii. 251. 

 J Eschscholtz, op. cit. 

 Travels, iv. 228. 



crabs, and worms. Even large fishes are some- 

 times found entangled amongst the arms and 

 tentacules. They are probably killed by the 

 peculiar excretion which covers the surface of 

 these organs, and which produces a stinging 

 effect on man. The long filamentary appen- 

 dages which hang from the margins of the disc 

 in Carybdea rxnd others, are covered with a 

 glutinous matter to which passing objects ad- 

 here ; the animal has the power of stretching 

 them out and withdrawing them at pleasure, 

 and of so folding them inwards as to carry to 

 the mouth whatever may be attached to their 

 sides. It would appear that some species are 

 endowed with the power of discriminating the 

 food most suitable to their own nature. Gaede 

 remarks that he has never found fishes in the 

 stomach of medusa capillata, but often worms ; 

 while in that of medusa aurita there are fre- 

 quently fishes, rarely worms. In none of the 

 pulmograda have either masticatory or salivary 

 organs been discovered. 



The cirrigrada have, in the middle of their 

 lower surface, a large flask-shaped stomach, 

 the mouth of which is formed like a sucker. 

 There appears to be a communication between 

 this organ and the numerous tentacula which 

 surround the mouth, through minute canals. 

 The food consists of small animals, such as 

 entomostracous Crustacea; the undigested re- 

 mains of which are again ejected through the 

 mouth. 



IV. Circulation. No distinct circulating 

 system has hitherto been discovered in the 

 acalephae. But perhaps the peculiar apparatus 

 of radiating vessels connected with the gastric 

 cavities in the pulmograda, and the aquiferous 

 canals of the ciliograda, which seem to per- 

 form nearly the same functions as the vascular 

 system of higher animals, may be conveniently 

 and properly considered under this head. 



In the physograda, Eschscholtz saw what he 

 considered as the rudiments of a circulatipn ; 

 namely, distinct vessels arising from the roots 

 of the tentacula, and ramifying on the in- 

 ternal surface of the air-bladders ; but it does 

 not appear that he traced these further, or that 

 he saw the movements of a fluid within them. 



The vessels in the ciliograda, within which 

 a fluid is seen to move, are situated chiefly 

 beneath the cilia-bearing arches. This fluid is 

 supposed by most modern anatomists to be 

 merely water ; but by some it is regarded as a 

 peculiar fluid, the product of the animal's 

 digestive powers. If it be water only, the 

 canals in which it moves must be considered 

 as being analogous to those of the aquiferous 

 system of other classes of invertebrate animals, 

 which has been so fully illustrated by the re- 

 searches of Delle Chiaje,* and which is pre- 

 sumed to be subservient to the respiratory 

 function. The vessels in question arise in 

 Beroe from a vascular circle which surrounds 

 the intestine near the anus. They are eight in 

 number, and one runs beneath each cilia-bear- 

 ing arch, from one extremity of the body to 



* Mem. sur la Storia e notomia degli animali 

 senza Vertebre, 4to. Napoli, 1823-25. 



