144 



MEDUS/E OF THE WORLD. 



part of the manubrium near the base consists of 4 radially situated masses of large, highly 

 vacuolated, entodermal cells, through the midst of which the 4 radial-canals extend downward 

 into the stomach. These cells are indeed only the entodermal walls of the radial-canals (plate 

 14, fig. 13). The stomach is large and quadratic in cross-section. The cruciform mouth is 

 situated at the extremity of a short neck and is surrounded by a row of nematocyst-bearing 

 knobs (plate 15, fig. 12). The gonads are developed upon the sides ot the stomach, where 

 they occur in the form of a double, longitudinal, swollen region in each adradius. Their 

 outer surfaces are smooth. The entoderm of the stomach is dull-yellow or orange, or dull- 

 vellow streaked with orange. The tentacle-bulbs sometimes contain a little entodermal 

 orange pigment. The ocelli upon the tentacles are dark-brown or orange. 



Hydroid and young medusa. The hydroid (fig. 76) was found by Brooks, 1883, on piles 

 of a wharf at Morehead City, North Carolina. It is a Dendroclava and closely related to D. 

 dohrnii Weismann. The stems of the hydroid are from 8 to 10 mm. in height and bear 

 large, terminal hydranths. There are also numbers of short, side branches which terminate in 

 hydranths. The main stem and the side branches are incased in a loose, cylindrical pen- 

 sarc, which is thick and becomes mcrusted with foreign matter. The pensarc is not an- 

 nulated, and terminates abruptly by a sharp collar immediately below each hydranth. The 

 hydranth or feeding-polypite is long and fusiform and bears from 18 to 20 short, thick, 

 filiform tentacles, which are arranged in three or more indefinite rows or whorls. The medusa- 

 buds originate upon the sides of the stem at the bases of the hydranths. Each medusa-bud is 



borne upon a short stalk or peduncle and is closely 

 invested by a thin capsule of perisarc. When set free 

 the young medusa has 8 tentacles. The manubrium is 

 cone-shaped and there is a large peduncle formed of 

 highly-vacuolated cells. 4 prominent, nematocyst bear- 

 ing knobs surround the mouth. The hydranths are pale 

 yellowish-red. 



This medusa is found from the coast ot Cuba to the 

 southern coast of New England, being about equally 

 abundant in the northern and southern limits of its range. 

 It is very common in the Bahamas and at Tortugas, 

 Florida. In Charleston Harbor, South Carolina, it is 

 commonly infested by larvae of Cunoctantha octonaria 

 McCrady, although it appears to be quite immune from 

 this parasite in other places. I can detect no specific 

 distinctions between this medusa and "Turntopsis [>ol\- 

 cirrka," which is occasionally seen off the Atlantic coast 

 of France and German}'. This form is well figured by 

 Keferstein, 1862, and Hartlaub, 1897, who are the only European students who have observed 

 the medusa on the eastern side of the Atlantic. 



Rittenhouse, 1907, has made an elaborate study of the development of T. nutricula. The 

 ova develop in the ectoderm of the 4 interradial sides ot the manubrium. The primitive ova 

 grow by the absorption ot ovarian cells around them, as is common in other hydromedusae. 

 The yolk-spheres in the ovum are formed from the ovarian cells which it absorbs. About 20 to 

 35, rarely 50 or more, eggs are discharged into the water by the muscular rupture of the ovar- 

 ian walls between 5 and 6 o'clock in the morning. The discharged eggs are spherical, o.i 16 

 mm. in diameter and have no membrane. They are yellowish-white, heavier than sea-water, 

 and opaque. The outer layer of finely-granular ectoplasm is distinct from the coarsely gran- 

 ular, yolk-laden endoplasm. Soon after being discharged the egg gives off two polar bodies 

 and is fertilized. Segmentation is total and approximately equal. The first two segmentation 

 planes are meridional and the third equatorial. The blastomeres remain quite far apart, 

 touching only slightly. After this the cleavage becomes remarkably irregular, recalling the 

 extraordinary condition observed by Hargitt in Pennaria. A solid morula is formed, which has 

 no central segmentation cavity and which resembles a loosely-connected mass of irregularly 

 grouped cells rather than an embryo of any metazoan. The cleavages follow one after another 

 at intervals of 20 to 30 minutes. 



I''K,. 75. -Turrtlopm nutrtculti, after Brook 

 Mem. Boston Soc. Natural History. 



