20 MEMORIAL PAMPHLET SHOWING CERTAIN DRAWINGS 



Pelagia cyanella Pron and Lesueur. 



Medusa pelagica, LINNE, 1758, Systema Nature, Ed. 10, p. 660. 



Medusa pelngica, LINNE, 1766, Systema Naturae, Ed. 12, p. 1098. 1788 (Gmelin), tomus I, pars 6, p. 3154. 



Pelagia cyanella, PERON ET LESUEUR, 1809, Ann. Mus. Hist. Nat. Paris, torn. 14, p. 349, No. 66. 



Dianaea cyanella, LAMARCK, 1817, Hist. Anim. sans vert., tome 2, p. 507. 



Pelagia cyanella, ESCHSCHOLTZ, 1829, Syst. der Acalephen, p. 75, taf. 6, fig. i. Bosc, 1830, Hist. Nat. des Vers., Ed. 2, tome 2, 

 p. 140, plate 17, fig. 3. AGASSIZ, L., 1862, Cont. Nat. Hist. U. S., vol. 4, pp. 128, 164; Ibid., 1860, vol. 3, plate 12, 

 figs. 1-16. AGASSIZ, A., 1865, North Amer. Acal., p. 47, fig. 68. HAECKEL, 1880, Syst. der Medusen, p. 507. VAN- 

 HOFFEN, 1888, Bibliotheca Zoologica, Bd. i, Heft. 3, p. 22. BIGELOW, 1890, Johns Hopkins Univ. Circ., vol. 9, No. 80, 

 p. 66. HARGITT, 1904, Bull. U. S. Bureau of Fisheries, vol. 24, p. 70, plate 7, fig. I. 



This American medusa is very closely related to the European P. noctiluca, of which it 

 is apparently only a local variety. 



Bell about 40 mm. high and 50 mm. broad; somewhat fuller than a hemisphere, being a 

 little less broad at margin than a short distance above. Numerous small wart-like nemato- 



O 



cyst capsules are sprinkled thickly over the exumbrella and are especially thick in a zone at 

 about mid-height of bell; these protuberances are reddish in color and tend to be arranged in 

 radiating lines. 8 very long, highly contractile, hollow tentacles alternate with 8 marginal 

 sense-organs. Each sense-club is set within a niche between two adjacent lappets and is 

 protected on the outer side by a partial web between the lappets. The club is hollow and has 

 no ocellus, but contains a terminal, entodermal mass of crystalline concretions which are deeply 

 pigmented. 1 6 marginal lappets, hemispherical in shape. There is a long, narrow, 4-sided 

 proboscis, the radial corners of which extend downward as 4 long, flexible mouth-arms, the 

 free edges of which are complexly crenulated. The proboscis, together with the mouth-arms, 

 or palps, is about 3 times as long as bell-height. There are 4 complexly folded horse-shoe- 

 shaped gonads in interradial positions upon the floor of the subumbrella, and immediately 

 centripetal to them are 4 subgenital pits or cavities extending inward from the outer surface 

 of the subumbrella. The quadrangular ossophagus leads into a circular, disk-shaped, central 

 stomach which gives rise to 16 radial pouches extending outward in the radii of the sense- 

 organs and tentacles. Each of these pouches gives off" a pair of unbranched, curved canals 

 which enter the lappets, but do not torm a ring-sinus. There are 16 well-developed strands ot 

 radiating muscle fibers in wall of exumbrella ad)acent to gastrovascular cavity. These extend 

 outward in the radii of the tentacles and sense-organs, and fork as they approach the bell-margin. 



The color is quite variable, sometimes bluish, sometimes slightly yellowish. Exumbrella 

 and mouth-arms sprinkled over with brownish-red nettlmg-warts, tentacles reddish-purple. 



This species is found among the West Indies and Florida Reefs, and in summer it may 

 drift northward in the Gulf Stream so as to appear off the southern coast of New England 

 from July to September. 



L. Agassiz, 1860 and 1862, found that the planulae of this species, as in P. noctiluca, 

 develop directly into medusae without going through a sessile scyphostoma stage and without 

 alternations of generations. The planulae are set free into the water where each develops into 

 a single medusa. The minute details of the development have been worked out upon Pelagia 

 noctiluca by Metschnikoff, 1886 (Emb. Stud, an Medusen, Wien.), and by Goette, 1893 

 (Zeit. fur wissen. Zool., Bd. 55, pp. 659-692). The gastrula is formed by invagination. The 

 first pair of radial stomach-pouches appear, according to Goette, as outpocketings from the 

 entoderm and these are quickly followed by another pair from the ectoderm of the throat- 

 tube, the two latter being 90 away from the former. The ectodermal pouches then give rise 

 each to two side branches and soon thereafter the entodermal do the same. Thus the cen- 

 tral stomach comes to have 12 radial pouches. 4 more radial pouches are soon formed 

 from the ectodermal pouches, so that the young medusa finally possesses 16 radial pouches. 

 It follows in adult medusa that the center of the exumbrella side of the central stomach is derived 

 from entoderm. 2 diametrically opposed, perradial pouches are ectodermal in origin and the 

 other 2 are entodermal. The 4 interradial pouches are ectodermal, and of the 8 adradial 

 pouches, 4 are ectodermal and 4 entodermal. The wall of the oesophagus is of ectodermal 

 origin. The young medusa soon develops 8 lobes which bifurcate, giving 16 marginal lap- 

 pets. The 8 marginal sense-organs develop before the tentacles. The mouth is at first a sim- 

 ple, round opening at the center of the crater-like ectodermal depression. It soon acquires 

 4 lips, but the mouth-arms do not develop until a later stage. It is probable that the ecto- 

 derm does not take so large a share in the formation of the stomach-pouches as Goette sup- 

 poses (see Clirysaora and Aurellia). 



