MAYEK : MEDUSAE FEOM THE TORTUGAS, FLORIDA. 43 



formed from both ectoderm and entoderm in the manner commonly observed 

 in Hydroids, and in the medusa of Sarsia ; for it is necessary, if organs be 

 homologous, that they have a similar origin. It has occurred to us, however, 

 that Chun may be mistaken in this conclusion, and that his statement may be 

 more a matter of definition than of fact; for it may well be that, in the course 

 of phylogeny, the entoderm has come to take less and less part in the formation 

 of medusa buds, until finally, as in the case of Bougainvillia niobe, it has 

 abandoned all share in their formation. Considered from the physiological 

 standpoint it may be that in B. niobe the ectoderm of the parent proboscis 

 being very thick, there is an abundance of cells from which to form the bud 

 without having resource to those of the deep-lying and somewhat inaccessible 

 entoderm. "When set free the young medusa possesses 4 radial tentacles. The 

 bell of the medusa is transparent, and the entoderm of the proboscis and ten- 

 tacle bulbs is rosin-yellow. 



Found in Nassau Harbor, New Providence Island, Bahamas, in March, 

 1893. 



It is interesting to notice that Hartlaub (1897 ; Hydromedusen Helgolands) 

 has shown that the sex cells of BougainviJlia superciliaris are first found in the 

 entoderm of the young medusa, and that as development proceeds they pass 

 into the ectoderm, where they become mature. It is possible that the cells 

 which give rise to the medusa buds of Bougainvillia niobe are similarly derived 

 from the entoderm of the young medusa. We have not seen the young and 

 immature medusa of B. niobe, and in the mature animal the supporting la- 

 mella between the ectoderm and entoderm of the proboscis is very distinct and 

 unbroken, and we have never succeeded in discovering any cells which were 

 passing through it. 



Margelis carolinensis, Agassiz, L. 



Hippocrene carolinensis, McCradj% J., 1857, Gynm. Cliarleston Harbor, p. 62, PI. 10, 



Figs. 8-10. 

 Margelis carolinensis, Agassiz, L., 1862, Cont. Nat. Hist. U. S., Vol. IV. p. 344. 



In the Tortugas and Charleston Harbor examples of this species, the ento- 

 derm of the tentacle bulbs and of the proboscis is of a delicate sage-green color ; 

 while the gonads are cream-colored, and the tentacular ocelli dark-brown or 

 black. In northern examples of this medusa, found at Newport, Rhode Island, 

 and Naushon, Massachusetts, A. Agassiz describes the color of the tentacle 

 bulljs as brilliant red surrounded by a green edge bordered with light 

 yellow; and the digestive cavity as brick-red, or green. No such brilliant 

 coloration has been seen in the southern specimens. The medusa is not very 

 common a.t the Tortugas, being met with only occasionally during the summer 

 months. In Charleston Harbor, South Carolina, however, it is extremely 

 abundant. 



VOL. XXXVII. — NO. 2. 4 



