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, 1860. 
(?) Alcinoé, Ranc, 1828, Mem. Soc. d’Hist. Nat. de Paris, tome 4, p. 168. 
(?) Mnemia, EscuscHo.tz, 1829, Syst. der Acalephen, p. Vv, 31. 
nemiopsis, Acassiz, L., 1860, Cont. Nat. Hist. U. S., vol. 3, pp. 269, 290.— 
Acassiz, A., 1865, North Amer. Acal., p. 19.—Cuun, 1880, Ctenophoren Golfes 
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. 1, Abhandl. 4, p. 59. 
GENERIC CHARACTERS. 
This genus of the Lobate 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 Alcinoé vermiculata 
Rang, 1828, found in April in the entrance to the Bay of Rio Janeiro, 
Brazil, is identical with Agassiz’s genus Munemiopsis. 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 
schweiggert. 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 Alcinoé rosea. JI am strongly 
inclined to believe that Agassiz’s Munemiopsis should be called Alcinoé, 
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, Acassiz, A., 1865, North Amer. Acalephe, p. 20, figs. 22-24.— 
FewkeEs, 1881, Bull. Mus. Comp. Zool. at Harvard Coll., vol. 8, No. 8, p. 173: 
plate 8, figs. 1-11; also, Ibid., vol. 9, p. 291, plate 1, figs. 1-9.—Cuun, 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.—Lituiz, R. §., 1908, Amer. Jour. Physiol., vol. 21, p. 200. 
