398 MEDUSAE OF THE WORLD. 



The type species is the very abundant Aglaura hemistoma Peron and Lesueur, found in 

 all warm oceans. There are many closely related "varieties," the extremes being A. nausicaa, 

 with a very short peduncle and A. laterna or A. octagona with long, tapering, slender peduncle. 

 The typical A. hemistoma is an intermediate form. I wholly agree with Vanhoffen, 1902, 

 in the belief that there is but one species and that this should be called A. hemistoma, for 

 the peduncle is provided with longitudinal muscles and may be twisted from side to side, and 

 to a limited extent contracted or elongated. Moreover, the bell may become "lantern-shaped," 

 "8-sided," "egg-shaped," "narrow," or "wide" dependent upon its state of contraction. 

 Bigelow, 1909, concurs in the opinion that A. hemistoma is the only known species. 



GENERIC CHARACTERS. 



Aglaurinae with 8 gonads upon the peduncle, not upon the subumbrella. 



The development of Aglaura hemistoma has been studied by Metschnikoff, 1886. It is 

 direct, the actinula-like larva being transformed into the medusa; the tentacles of the medusa 

 being those of the actinula and making their appearance before the bell begins to develop. 



Aglaura hemistoma Pe"ron and Lesueur. 

 Plate 46, figs. 4 and 5; plate 49, figs. 3 to 7; plate 50, fig. II. 



Aglaura hemistoma, Peron et Lesueur, 1809, Annals. Mus. Hist. Nat. Paris, tome 14, p. 351.— Gegenbaur, 1856, Zeit. fiir 

 wissen. Zool., Bd. 8, p. 248, taf. 8, fign. 13-15. 



Aglaura peronii, Leuckart, 1856, Archiv. fiir Naturgesch., Jahrg. 22, p. 10, taf. 1, figs. 5-7. 



Aglaura hemistoma, Haeckel, 1879, Syst. der Medusen, p. 275, taf. 16, fign. 3, 4.— Metschnikoff, F.., 1886, Embryol. Studien 

 an Medusen, Wien, pp. 23 (egg), 35 (segmentation), 60 (entoderm), 93 (development of medusa), taf. 7, fign. 1-31; taf. 8, 

 fig. 1; 1886, Arbeit. Zool. Inst. Wien, Bd. 6, p. 245, taf. 23, figs. 21-23.— Mayer, 1900, Bull. Mus. Comp. Zool. at Har- 

 vard College, vol. 37, p. 65, plate 25, figs. 79, 80; 1904, Mem. Nat. Sci. Brooklyn Institute Museum, vol. 1, p. 26, plate 4, 

 fig. 34. — Vanhoffen, 1902, Wissen. Ergeb. deutsch. Tiefsee Expedition, Dampfer Valdivia, Bd. 3, Lfg. 1, p. 78.— 

 Browne, 1904, Fauna and Geog. Maldive and Laccadive Archipel., vol. 2, p. 739; 1906, Trans. Linnean Soc. London, 

 ser. 2, Zool., vol. 10, p. 176.— Harc.itt, 1904, Bull. U. S. Bureau of Fisheries, vol. 24, p. 55; 1902, Biol. Bulletin Woods 

 Hole, vol. 4, p. 14, fig. 1.— Bigelow, H. B., 1909, Mem. Mus. Comp. Zool. at Harvard College, vol. 37, p. 119, plate 

 2, fig. 6. 



Aglaura ciliata, Perkins, 1906, Year Book of the Carnegie Institution Washington, No. 4, 1905, p. 115 (medusa from Tortugas, 

 Florida, with markedly ciliated mouth).— 1908, Papers from Tortugas Laboratory of Carnegie Inst, of Washington, 

 vol. 1, p. 148, plate 3, figs. 14-16. 



Bell is 3 or 4 mm. in diameter and 4 to 6 mm. high ; bell-walls vertical, exceedingly thin, 

 the top quite flat; although thin, the bell is very rigid and swimming is accomplished 

 almost entirely by the movements of the large and powerful velum. About 48 to 85 solid, stiff 

 tentacles which are usually found to be broken off short; when present, however, they are 

 seen to be about three-fourths as long as bell-diameter and their outer ends are slightly 

 club-shaped. 8 small, free sensory-clubs, about midway between the 8 radial-canals, are 

 definitely arranged in reference to the tentacles (see fig. 11, plate 50). Each sensory-club is 

 surrounded by a number of sensory hairs. There is a single concretion within the club. 

 Sometimes this concretion appears to exhibit facets but more often it is simply oval in shape. 

 The 8 radial tubes are straight and very narrow. The stomach is mounted upon a conical 

 peduncle somewhat shorter than the bell-radius. The stomach is flask-shaped and there are 

 4 prominent, more or less ciliated lips. The 8 sausage-shaped gonads are situated upon the 

 peduncle at the places of juncture of the 8 radial-canals with the stomach. The entodermal 

 core of the stomach and occasionally the entoderm of the gonads display a red-brown pigment. 



Common in surface-tows in all warm seas. Abundant in the Atlantic, Mediterranean, 

 Red Sea, Pacific, and Indian Oceans, but unknown from Polar Seas. 



The development of Aglaura hemistoma has been studied by Metschnikoff, 1886. The 

 egg is 0.09 mm. in diameter and is cast out into the water between 1 1 and 1 o'clock (mid-day) 

 in April, in the Mediterranean. The segmentation is total but very unequal, the cells of the 

 animal pole being much smaller and dividing more rapidly than those of the vegetative pole of 

 the larva. Soon the small, rapidly dividing cells of the animal pole extend over the sides of the 

 spherical larva and completely inclose the few, large, central cells. These small cells become 

 the ectoderm, while the large central cells give rise to the entoderm. The solid planula then 

 becomes ciliated and elongates, so as to become rod-like with cylindrical sides and rounded 

 ds. The central entoderm then consists of a single row of 10 to 15 disk-like cells, incased by 



en 



