^ 61. THE ACALEPHAE. 65 



CHAPTER V. 



DIGESTIVE APPARATUS. 



§ 61. 



The digestive apparatus of the Acalephae is formed after several very 

 different types. The mouth is sometimes single and central, or there may 

 be many of them. It is often surrounded with arms and retractile filaments, 

 which are endowed with the prehensile and nettling organs just described. 



The digestive cavity, which is always lined with ciliated epithelium, haa 

 distinct walls, which are united immediately to the parenchyma of the 

 body, leaving, therefore, no surrounding cavity. 



With those having a single mouth the stomach is of a variable size, and 

 has often caecal appendages. With Beroe,'-^^ the mouth is very large and 

 free from tentacles, and opens into a very spacious stomach which occu- 

 pies nearly the whole body. But with Cestum, Cydtppe and LesiieuriUf 

 the stomach is small, and appears like a cavity in the body ;'^' and with 

 Cytaeis, Thaumafitias and Geryonia, it is likewise small, and has the 

 shape of a tubular projection.*'^' 



That of Medusa has four saccular folds,**' that of Pelagia^^^ six, and that 

 of Cyanea thirty-two.**^' 



When the mouths are numerous, either, as in the Rhizostomidae,"' there 

 are many canals which conduct the food through the arms upon which the 

 mouths are situated into the central stomach ; or, as in the Siphonophora, 

 each mouth opens into a particular tubular stomach. With these last, 

 however, a certain number of their tentacles are hollow, and have a mouth 

 at the extremity. As it has been observed that these suck in food and 

 digest it, their orifices have been regarded as mouths, and their cavities as 

 stomachs.***^ 



1 üfiVneSdward», Ann.d.Sc. Nat. XVI. pp. 5, 6. Phi/ippi, however, affirms that in this last 



'■i Eschschottz, loc. cit. Taf. I. II.; aud Milne genus these canals are organs of absorption, and that 



Edwards, loc. cit. PI. III. the true stomach, which has a simple mouth, is 



3 fVill, loc. cit. Taf. II. concealed at the base of the tentacles (loc. cit. p. 



4 Baer, in MeckePs deutschs. Arch. VIII. 1823, 63, Taf. V. fig. 10). 



Taf IV. fig. 2; also, Ehrenberg in Abhandl. d. I think, however, that this opening belongs to the 



Berl. Akad. 1835, Taf. III. fig. 1. respiratory system, as also does a similar opening 



5 fVagner, Icon. zoot. Tab. XXXIII. fig. 5. in p'eleila and Porpita, which Lesson (Voyage de 



6 Gaede, loc. cit. Taf. II. Duperrey, loc. cit. p. 49, 56, No. 6, fig. B. ; aud No. 



7 Eysenhardt, Nov. Act. physico-med. X. part 7, fig. C. 0.) has regarded as a mouth. 



II. p. 391, Tab. XXXIV. fig. 1 {Rhizostomum The tubular tentacles of these animals are noth- 



Cuvieri). ing but stomachs ; and Lesson himself has called 



8 Tliis is so, for examples, in £)i;)A!/ei (/F!7/, loc. them "poches stomacales," since they digest 

 cit. Taf. II. fig. 22) ; in Physalia {Olfers Abhandl. food. It would, moreover, be strange that these 

 d. Berl. Akad. 1831, p. 162, Taf. I.) ; in Stephana- organs, which, in Physalia, have been admitted to 

 mia {Miine Edwards, Ann. d. Sc. Nat. XVI. PI. be stomachs, should perform another function in 

 VII. IX. X.) i and in Physophora {Philippi, Physophora, Velella, and Porpita, where their 

 MuUer's Arch. 1843, Taf. V. fig. 1,4). structure is the same. But further researches are 



(Loc. cit. p. 316.) On a preceding page he says : miferous system, which opens above its gelatinous 



"That this may be the case seems probable when disc, notwithstanding these openings." (p. 248.) 



we consider the relation of the two sorts of appa- This point, fully as interesting from its zoological 



ratus in the two types. The upper nervous ring in importance as from its morphological relations, 



Sarsia bears the same relation to the central ali- can be settled only by a knowledge of the embryolr 



mentary cavity, and to the pigmented disc, that the ogy of these animals. — Ep. 

 ganglion and eye-speck of Beroi bear to the chy^ 



6^ 



