NARCOMKDUS.E — -SGINA. 



451 



distinct and can not be merged. ALginopsis is probably derived from /Eginura by the reduction 

 of half of its tentacles and bears the same relation to JEginura that Solmundella does to Mgina. 



Maas, however, proposes a classification which avoids the minute distinctions of Haeckel's 

 system, and his arrangement is far simpler and more convenient. 



A genus may be looked upon as a somewhat crudely gathered collection of near blood- 

 relatives, and their general relationship is often rendered more apparent by permitting them all 

 to remain under one broad designation than by subdividing them upon a basis of slight dis- 

 tinctions, thus obscuring the fact of their relationship. Systematic zoology will be better 

 advanced by a classification which indicates relationships, rather than bv one which points out 

 distinctions, and Haeckel's system, ingenious as it always is, is artificial in that it often widely 

 separates forms which are actually closely related. 



Cunarcha Haeckel is probably a larval stage of ALgma, wherein the 4 primary stomach- 

 pouches are not yet cleft by the insertion-roots of the tentacles. Cunarcha bears the same 

 relation to JEgina as Cunoctona does to JEginura. 



jEgina citrea Eschscholtz. 



JEgina eitrea + Mgina rosea, Eschscholtz, 1829, Syst. der Acalephcn, pp. 113, 115, taf. 10, fig. 3; taf. 11, fig. 4. 



&gjna rosea+ JEgina citrea, Haeckel, 1879, Syst. der Medusen, p. 338. 



JEgina citrea, Maas, 1905, Craspedoten Medusen der Siboga Expedition, p. 71, taf. II, fig. 72; taf. 13, fign. 79-82. — Bkielow, 



H. B., 1909, Mem. Museum Comp.Zool. at Harvard College, vol. 37, p. 73, plates I, 14. — Vanhoffen, 1908, Narcomedusen 



der Valdivia Expedition, p. 50. 



Bell 20 to 50 mm. wide, hemispherical, gelatinous substance thick at apex but very thin 

 at margin. 4 stiff, tapering tentacles, about as long as bell-diameter, project from the sides of 

 bell in a zone about midway between margin and apex. A deep, radial furrow extends up 

 from bell-margin to base of tentacle; its bottom is lined by a thickened mass of ectoderm, con- 

 taining nematocysts, called the peronium. This 

 peronial strand becomes considerably swollen 

 immediately under the base of each tentacle 

 forming a cushion-like support tor the latter. 

 Tentacles solid, their entoderm consisting of 

 vacuolated chordate cells continuous with the 

 entoderm of the stomach. 



There are typically 8 marginal sensory- 

 clubs, 2 in each quadrant between tentacles, but 

 Vanhoffen records 16 in one quadrant. Velum 

 well-developed with powerful circular muscles. 

 Stomach wide, flat, lenticular, its periphery giv- 

 ing rise to 8 radiating pouches, 2 between each 

 pair of tentacles. These pouches are rectangular 

 with rounded angles and are nearly as long as 

 radius of central part of lenticular stomach. The 

 8 pouches are separated one from another by 8 long, narrow clefts and there is a small notch 

 at the middle of the outer edge of each lappet. Mouth simple, circular. The peripheral 

 canal-system consists of 4 separate loops, each loop being composed of a narrow vessel, 

 extending outward from the edge of the stomach on one side of a tentacle and then down on 

 the same side of a peronium, then along a quadrant of the margin, to ascend along the side of 

 another peronium and to reenter the stomach on the adjacent side of a tentacle 90 away from 

 its place of origin. The gonads are developed in the ectoderm of the subumbrella wall of the 

 stomach around the peripheral parts of the stomach-pouches. 



The entoderm of the stomach and its pouches are citron-yellow or rose-red. Many 

 Trachymedusae and Narcomedusae are greenish by reflected, and red by transmitted, light and 

 this may account for the differing descriptions of its color. 

 Found in the tropical Pacific. 



Vanhoffen, 1908 (Narcomedusen der Valdivia Expedition, p. 48, taf. 1 and 3), records the 

 capture of 19 specimens of an ALgma in the tropical Atlantic and Indian Oceans between 

 depths of 2,000 fathoms and the surface. He calls this medusa Angina rosea, but it lacks the 



Fig. 299. — Mgina citrea, after Eschscholtz, 1829. 



