TRACHYMEDUSjE AGLANTHA. 



403 



apex. About 80 to 100 long, slender tentacles having only a moderate degree of contracta- 

 bility. These tentacles are very brittle and in medusae caught in tow-nets are usually broken 

 off very near to bell-margin, leaving only short stumps. In the majority of individuals there 

 are 4 lithocysts (plate 49, fig. 2') situated 90 apart and midway between every alternate pair 

 of radial tubes. I have, however, found individuals with 3, 5, 6, and 8 lithocysts, and the figure 

 shows one having 8 lithocysts. It is probable that the normal complete number is 8, but that the 

 concretions are easily lost. Velum large, provided with powerful muscles. 8 very narrow, 

 straight radial-canals and a simple, slender, circular vessel. A long, spindle-shaped, gelatinous 

 peduncle extends from inner apex of subumbrella almost to level of bell-margin. '8 radial 

 tubes extend straight down this peduncle to the stomach, which is short and cylindrical and 

 provided with 4 prominent lips. 8 sausage-shaped gonads arise from the sides of the 8 radial 

 tubes near inner apex of subumbrella and hang downward into cavity of bell. Females only 

 have been observed. The ova are large and prominent. The bell is translucent and dis- 

 plays a dull-horny or iridescent appearance. The gonads are of a milky, yellow-white 

 color and the entoderm of the stomach and tentacles is pink. 



Young medusa. — In young medusa; about 4 mm. in height, the bell is quite globular, the 

 tentacles are much less numerous than in the adult, and the gonads have not yet made their 

 appearance. Moreover, the peduncle is at this stage very little developed, so that the mouth 



255- 



254- 



Fig. 154— Aglantha globuligera, after Haeckel, in Das System der Medusen. 



Fig. 255. — "Aglantha elata," after Haeckel, in Syst. der Medusen. 



Fig. 256. — Aglantha ignea, after Vanhdffen, in Tiefsee Expedition Vahlivia. 



projects but a little distance downward from the inner apex of the bell-cavity. As the medusa 

 develops, the bell increases relatively in height, the tentacles become more numerous, the 

 peduncle elongates, and the gonads finally make their appearance. 



Aglantha camtschatica described by Brandt, 1838, from the North Pacific, is probably 

 identical with A. digitate of the North Atlantic. 



This medusa is extremely abundant all over the North Atlantic, north of latitude 45 . It 

 does not appear to extend south of latitude 40 in the Atlantic. In common with other Arctic 

 species, it makes its appearance in great numbers upon the southern coast of New England 

 early in the spring, but disappears before June. It remains common throughout the summer, 

 however, in the harbor of Eastport, Maine. The Plankton Expedition, of 1889, met with great 

 swarms of this medusa between the Hebrides and Greenland during July. Browne found it in 

 Fowler's collection from the Bay of Biscay, made at a depth of 100 fathoms. 



Browne calls medusae with 8 lithocyst-clubs "A. rosea," while A. digitate he would restrict 

 to include medusae with only 4 of these organs. I believe that the medusa usually becomes 



