280 



MEDUSA of the world. 



developed, spindle-shaped gonad upon each of the 17 radial-canals near the middle of its 

 length. 17 short, straight, blindly ending, centripetal canals alternated with the 17 complete 

 radial-canals. In this specimen the centripetal canals lacked gonads, but in other individuals 

 gonads were observed upon the centripetal canals even before they had fused with the stomach. 

 In the specimen under consideration there were (17 X 4) 68 tentacles alternating with 68 

 closed lithocysts each containing a single oval concretion. The velum is wide and muscular. 

 The simplest medusa observed had a hemispherical bell about I mm. wide, 8 tentacles (4 

 radial and 4 interradial); central stomach with 4 lips, no gonads, no centripetal canals, and 

 no lithocysts. 



This medusa occurred in large numbers for a few days only early in March, 1882, in the 

 Harbor of Suakin,^Red Sea. 



Fig. 151. — Gastroblasta timida, after Keller, in Zeit. fur wissen. Zool. 



Gastroblasta raffaelei Lang. 



Phialidium variabiles Davidoff, 1 88 1 , Zool. Anzeiger, Bd. 4, p. 620, I fig. 



Gastroblasta raficelei, Lang, 1886, Jena. Zeit. fiir Naturwissen., Bd. 19, p. 735, taf. 20, 21, 32 fign. 



(>)Euco/>e polygastrica, Metschnikoff, E., i870,Verhandl.kaiserlichen Gesell. Freunde Naturwissen. Moskau, tome 8, p. 346, 

 taf. 4, figs. 2, 4; Arbeit. Zool. Inst. Wien, 1886, p. 260. 



This remarkable medusa was found in great numbers in August and September, 1885, 

 at Naples, Italy. It is characterized by having usually more than one stomach, a variable 

 number of radial-canals, a well-developed ring-canal, and a number of hollow, bulbed tentacles 

 of various ages. Upon the bell-margin, between the tentacles, are simple, closed lithocysts, 

 each with a single concretion. These concretions are of various ages. 



The simplest medusae had 8 well-developed tentacles and 10 small, as yet undeveloped, 

 tentacle-bulbs. There were also 10 lithocysts upon the bell-margin between the tentacles. 

 Near the center of the subumbrella were 4 manubria, 1 large, 2 small, and I very small 

 (as yet undeveloped). The functional manubria always have 4 lips; the 2 oldest are joined 

 by a chymiferous canal, and this forks so that 4 main radial-canals reach the circular vessel. 

 The 4 oldest tentacles are at the ends of these 4 main radial-canals. The disk is never exactly 

 circular, but more or less elliptical, the long axis of the ellipse being in the line of the vessel 

 which connects the 2 oldest manubria. Velum well developed, disk flat and thin. 



This medusa often reproduces itself by fission. The plane of division is at right angles to 

 the long axis of the ellipse and passes between the oldest and next oldest manubrium. When 

 about to divide, the oldest lithocyst divides into two and the cleft proceeds inward at this 



