LEPTOMEDUS.E — GASTROBLASTA, EUCHEILOTA. 281 



point until the medusa is completely cut into halves, the one being a reflection of the other. 

 Each then develops new radial-canals, manubria, and tentacles, the new radial-canals budding 

 from the ring-canal and growing inward. When the original form has been restored, a new 

 fission may take place. This is not a constant process, however, but is subject to much vari- 

 ability, for new radial-canals may grow inward from the ring-canal in the regions of the older 

 tentacles, and these new canals may fuse with the old canal-system and develop manubria. 



Thus the largest medusa seen had a diameter in its long axis of 4 mm. and in its short 

 axis of 2.7 mm. There were 26 well-developed and 17 rudimentary tentacles, 34 lithocysts 

 scattered between the tentacles, 20 radial and centripetal canals, 9 complete and 7 rudimentary 

 (undeveloped) stomachs. The stomachs are urn-shaped with thick walls; the mouth-tube 

 is elongate, 4-sided, and with 4 well-developed lips. Gonads sometimes develop upon one or 

 more of the radial-canals, the mature sperm or ova being ectodermal. These gonads occur 

 near the middle of the canals upon which they develop. 



The medusa may be regarded as primitively 4-rayed, but this condition is masked by its 

 peculiar processes of asexual reproduction and growth. It is described in detail bv Lang. 



Gastroblasta ovalis. 



Plate 35, figs. 7 and 8. 

 Mullioralis oralis, Mayer, 1900, Bull. Museum Comp. Zool. at Harvard College, vol. 37, p. 54, plate 39, figs. 129, 130. 



Adult medusa. — Bell quite flat, elliptical in outline, the major axis being 4 mm. and the 

 minor 2.4 mm. The gelatinous substance is not very thick and is quite flexible. 20 to 25 short, 

 simple, coiled tentacles with well-developed basal bulbs. These tentacles are only about half 

 as long as the minor axis of the bell. Neither lateral nor marginal cirri. Lithocysts slightly 

 more numerous than the tentacles, usually 1, but occasionally 2, being found between each 

 successive pair of tentacles. In each lithocystis a single, spherical concretion. Velum simple 

 and quite broad. There is a slender circular vessel, and a single, straight, chymiferous canal 

 extends along the major axis of the bell. In the oldest medusae observed there were 4 man- 

 ubria, 2 equally developed large manubria on either side of the center of subumbrella, 

 upon the chymiferous canal; and 2 small manubria upon the same canal centrifugally away 

 from the larger manubria. There was thus no manubrium at the center of the subumbrella. 

 There were 2 small gonads upon the chymiferous canal immediately centrifugal from the 

 small manubria. 



The entoderm of the manubria and of the basal bulbs of the tentacles is an opaque, 

 glistening white. The supporting lamella of the bell is of a delicate green. 



Young medusa. — In the youngest medusa observed, there were but 2 manubria upon the 

 chymiferous canal on either side of center of disk. The major axis of the bell was 2.5 mm. and 

 there was no trace of gonads. About a dozen specimens of this medusa were captured at the 

 Tortugas, Florida, from June 30 to July 2, 1899, and none have been seen since that time. 

 It seems possible that the bell of the large medusa may divide by transverse fission, for one 

 individual was found in which there was a decided notch in the bell-margin extending inward 

 in the plane passing through the center of the subumbrella perpendicular to the main chymif- 

 erous tube. This notch appeared, however, upon only one side of the bell and may have been 

 due to accident. Apparently the main chymiferous canal is equivalent morphologically to 2 

 diametrically opposed radial-canals. 



Genus EUCHEILOTA McCrady, 1857. 



Eucheilota, McCrady , 1857, Gymn. Charleston Harbor, p. 85.— Agassiz, L., 1862., Cont. Nat. Hist. U. S., vol. 4, p. 353. — Mayer, 



1900, Bull. Museum Comp. Zool. at Harvard College, vol. 37, p. 56. 

 Euc/iilota, Agassiz, A., 1865, North Amer. Acal., pp. 74-76. — Browne, 1896, Proc. Zool. Soc. London, pp. 481, 484. 

 Euchilota=Phialium, Haeckel, 1879, Syst. der Medusen, pp. 179, 180. 

 Octanopsh, Fewkes, 1883, Bull. Mus. Comp. Zool. at Harvard College, vol. 11, p. 86. 

 Dipleuron, Brooks, 1882, Studies Johns Hopkins Univ. Biol. Lab., vol. 2, p. 139. 

 l y hialium, Bigelow, H. B., 1909, Mem. Mus. Comp. Zool. at Harvard College, vol. 37, p. 153. 



This genus was founded by McCrady, 1857, for Eucheilota ventricularis of the Atlantic 

 coast of the United States, 



