^.63. 



TUE ACALEPHAE. 



6T 



colored fluid and colored corpuscles ; and these corpuscles are not found 

 except in those vessels surrounding the aquiferous canals. 



Thei-e is no regular circulation, but the shifting motion of the blood 

 hither and thither is due to irregular contractions of various parts of the 

 body /I' 



CHAPTER VII, 



RESPIRATORY SYSTEM. 



§ 63. 



The entire body of the Acalephae' is traversed by canals which receive 

 "water from the stomach, or directly from without, and which is ejected 

 through openings upon the extremity of the body and on the margin of the 

 disc. 



These aquiferous canals are lined with a delicate, ciliated epithelium, by 

 means of which accidental particles of food or fgeces are quickly removed. 

 They have been regarded both as digestive and as sanguineous organs. 

 But that they are respiratory organs is highly probable, not only from their 

 structure, — the cilia producing a constant renewal of water, — but also from 

 the fact that they are surrounded by real sanguineous vessels. 



This aqueous circulation is oscillatory from one side of the body to the 

 other, being interrupted only by those contractions of the body which occur 

 :when fresh water passes from the stomach into the canals.*^* 



1 These new details upon the sanguineous system 

 •of the Acalephae are due to JVill (Horae tergest. 

 p. 34, and Froriep^s neue Not. No. 599, 1843, p. 

 ■66). In Beroe, he has been able to cleai-ly distin- 

 guish the sides of these vessels from those of the 

 aquiferous canals contained in their interior, for 

 the first are covered with numerous red pigment 

 .cells. 



The blood of this animal has a greenish hue, and 

 'Contains spherical or slightly elongated red corpus- 

 cles, with large nuclei. But, beside these, if ill has 

 found in Cydippe other nucleated cells of a green- 

 ish color. In' Polyxenia, thei'e is no sanguineous 

 system separate from the aquiferous canals, which, 

 in Cytacis and Geryonia are quite surrounded by 

 them. The vessels of Cephea contain brown cor- 

 puscles ; and Will has concluded that the reddish 

 threads found along the aquiferous canals of this 

 -animal, and which Ehrenberg (Abhandl. d. Berl. 

 Akad..l835, p. 195, Taf. VI. fig. 3,.^, and Muller's 

 Arcji. 1834,. p. 568) has taken for striated muscles, 

 are really blood-vessels. Profound researches must 

 decide the real relations, of the aquiferous canals to 

 the sanguineous system filled with a violet liquid 

 of Velella, as described by Costa (Ann. d. Sc. 

 HaX. XVI. p. 188, PI. XIII. fig. 3). It should be 

 mentioned that the blood-system of the Acalephae, 



* [§ 62, note 1.] A true circulatory system has 

 not been observed also by Dana (Struct, and 

 Class, of Zoophytes, 1846, p.- 12), by Forbes (Brit. 

 Naked-syed Medusae, 1848, p. 6), by Agassiz 

 (Contributions to the Nat. Hist, of the Acalephae 

 of North America, Mem. Amer. Acad. Boston, 

 1850, p. 260), and by Busch (Beobacht. üb. Anat. 



which Will has described with so much positive- 

 ness, is not verified either by Bergmann or Frey 

 and Leuckart (Beitr. p. 38), after numerous spe- 

 cial researches.* 



1 If, and especially with the Discophora, these 

 canals have been taken for digestive tubes, it is 

 because faeces and particles of food have been here 

 found, and which have been ejected through the 

 openings on the borders of the body. But the real 

 function of these openings is to discharge the water 

 unfit for respiration ; and it is only during the in 

 gestion of this li(|uid that these foreign particles are 

 thus introduced. This communication between the 

 respiratory and digestive systems reminds one of 

 the Polyps, where (as in the Anthozoa) the open- 

 ings in the stomach allow its contents to pass into 

 the cavity of the body, which last may be likened 

 to the aquiferous system. On the other hand, the 

 opinion that these canals are blood-vessels would 

 be supported by the Ctenophora, since here they 

 are filled with a red liquid ; but, according to Will 

 (Horaä tergest. p. 34), this liquid is not in these 

 canals, but in proper blood-vessels surrounding 

 them. He denies, also, that these blood-vessels of 

 the Ctenophora open upon the sui-face of the 

 body, or that the blood escapes outward mixed 

 with fajces. 



u. Entwick. einiger wirbellosen Seethiere, 1851, p. 

 13). It may, therefore, be concluded that these 

 animals have no system of this kind, and especially 

 so as Agassiz faded to notice it after the most inti- 

 mate research upon the Beröid Medusae (loc. cit. 

 p. 313), which were the objects of WiWs study. 

 — Ed. 



