26 CTENOPHORES OF THE ATLANTIC COAST OF NORTH AMERICA 



combs of cilia overlying them cease to beat and resume their rhythm 

 only when the muscles relax, for if the surface of the ctenophore be 

 pressed or stretched the ciliated combs of the stretched area are in- 

 hibited. Thus magnesium does not stimulate, but weakly subdues 

 ciliary movement; but its inhibitory effect upon nerves and muscles is 

 more marked, and it soon relaxes the muscles, thus lessening the mus- 

 cular tonus and reducing the pressure which is normally exerted by the 

 epithelium upon the cilia-bearing cells ; and then the cilia beat unhin- 

 dered as do isolated cells when separated from the epithelium. Thus 

 the so-called " converse relation between ciliary and muscular move- 

 ment " is due to mechanical causes, not to converse chemical effects of 

 the cations of sea- water upon muscles and cilia respectively. 



Genus MNEMIOPSIS L. Agassiz, i860. 



(?) Alcinoe, Rang, 1828, Mem. Soc. d'Hist. Nat. de Paris, tome 4, p. 168. 



(?) Mnemia, Eschscholtz, 1829, Syst. der Acalephen, p. v, 31. 



Mnemiopsis, Agassiz, L., i860, Cont. Nat. Hist. U. S., vol. 3, pp. 269, 290. — 

 Agassiz, A., 1865, North Amer. Acal., p. 19. — Chun, 1880, Ctenophoren (jolfes 

 von Neapel, p. 290; also, 1898, Ctenophoren der Plankton- Expedition, p. 25. — 

 Mayer, 1900, Bull. Museum Comp. Zool. at Harvard College, vol. 37, p. 9. — 

 MosER, 1908, Abhandl. Akad. Munchen, Suppl. Bd. i, Abhandl. 4, p. 59. 



GENERIC CHARACTERS. 



This genus of the Lobatae is closely allied to Bolinopsis, but is dis- 

 tinguished by having 4 deep, lateral furrows which extend upward from 

 the level of the mouth along the edges of the oral lobes to about the level 

 of the apical sense-organ. A lateral branch from the paragastric vessel 

 extends upward along each of these grooves, and numerous short, simple 

 tentacles arise along the length of this canal. The outer edge of an 

 auricle also extends upward along each groove and this edge is bordered 

 with numerous cilia. 



The type species is Mnemiopsis gardeni L. Agassiz, from Charleston, 

 South Carolina. 



Future studies will probably demonstrate that Alcinoe vermiculata 

 Rang, 1828, found in April in the entrance to the Bay of Rio Janeiro, 

 Brazil, is identical with Agassiz's genus Mnemiopsis. Certainly it 

 has all of the external characters of Agassiz's genus, but Rang does not 

 figure or describe its internal anatomy, so that there is a possibility that 

 we may be able to separate it generically from Mnemiopsis . Rang's 

 ctenophore was redescribed by Eschscholtz, 1829, under the name Mnemia 

 schweiggeri. Another species from the southern hemisphere in S. lat. 

 44° 12', W. long. 56® 30', north of the Falkland Islands, is described and 

 figured by Mertens, 1833, under the name Alcinoe rosea. I am strongly 

 inclined to believe that Agassiz's Mnemiopsis shovdd be called Alcinoe, 

 but I hesitate to act in the matter owing to our imperfect knowledge of 

 the forms described by Rang, Eschscholtz, and Mertens. 



Mnemiopsis leidyi A. Agassiz. (Figs. 20 to 46, plates 6 to 8.) 



Mnemiopsis leidyi, Agassiz, A., 1865, North Amer. Acalephae, p. 20, figs. 22-24. — 

 Fewkes, 1881, Bull. Mus. Comp. Zool. at Harvard Coll., vol. 8, No. 8, p. 173, 

 plate 8, figs, i-ii; also, Ibid., vol. 9, p. 291, plate i, figs. i-o. — Chun, C., 

 1898, Ctenophoren der Plankton-Expedition, p. 25. — Hunter, 1904, Biol. 

 Bulletin, Woods Hole, vol. 6, p. 324. — Parker, 1905, Jour. Exper. Zool., 

 vol. 2, p. 407. — Lillie, R. S., 1908, Amer. Jour. Physiol., vol. 21, p. 200. 



