TRACHYMEDUS.E CRASPEDACUSTA. 365 



ectoderm and entoderm taking part in its formation. Thus each polypite appears to give rise 

 to but one medusa, although the detachment of the medusa and future fate of the polypite has 

 not been observed. We must bear in mind that it is not yet certain that this hydroid is actually 

 the asexual generation of C. sowerbii. 



The young stages in the development of the free medusa, found in the lily-tank, have 

 been studied by Lankester, 1881 (Quart. Journ. Microscop. Soc. London, vol. 21, p. 194, 

 5 figs.). When the embryo is less than 1 mm. in diameter the body is globular with 8 very 

 small tentacles, 4 radial, 4 interradial, and 2 marginal lithocysts. The velum is present as a 

 diaphragm-like membrane at the bases of the tentacles; but inside of, and separate from, 

 the velum there is said to be a peculiar imperforate membrane which completely closes the 

 bell-cavity. The manubrium is well developed at this stage and there are 4 radial-canals. 



Haeckel (Jena. Zeitschift, Bd. 2) states that the subumbrella cavity in Geryoma forms as 

 a closed sac, and only later does the membrane closing it break through. This observation is 

 in accord with Lankester's studies on Craspedaeusta, but is opposed to the observations ot 

 Metschnikoff, Brooks, and others on Geryonidae. 



Romanes, 1880, 1881, found that the medusa is exceedingly intolerant of ocean water 

 and is injuriously affected by fresh water which is diluted with one-ninth of its volume of 

 ocean water. The medusa is strongly positive in its heliotropism, and during the day it is found 

 in the highest and most brightly lighted part of the tank, but it sinks to the bottom at night. 



In 188 1 Lankester found that the entodermal cells near the mouth are gland-cells and 

 produce a secretion. The cells of the mid-region of the stomach are inactive, but those of the 

 inner region of the stomach, near the place of origin ot the radial-canals, send out amoeboid 

 processes and engulf solid food particles into their protoplasm. A similar process of intra- 

 cellular digestion has been demonstrated by Metschnikoff and by Jeffery Parker in hydroids, 

 and in their medusae. 



Maas, 1907, finds that the medusa will pulsate spontaneously if even a small portion ot 

 the bell-margin be left intact. With margin completely removed no spontaneous pulsations 

 occur, but the central disk may still respond temporarily to stimuli such as NaCl, KC1, 

 mechanical shock, or electric current. The manubrium bends toward the cathode. Hargitt, 

 1908, finds that the normal medusa can not continue to pulsate it placed in distilled water, 

 but he does not determine whether this inhibition is due to lack ot sodium, etc., or to the 

 deficiency of oxygen. 



Cremer, 1907, made a study of the phenomena of rhythmical pulsation in Craspedaeusta, 

 using a galvanometer. He finds that the electromotive force ot the epithelial muscular system 

 of this medusa is nearly as great as in the muscles of warm-blooded animals. This seems 

 the more remarkable in view of the relative deficiency ot salts in the fresh water surround- 

 ing the medusa. Cremer points out a possible analogy between the action of the muscles 

 of this medusa in maintaining pulsation and the electric organs of electrical fishes in giving 

 shocks. 



Craspedaeusta kawaii. 



Limnocodium kawaii, Oka, 1907, Annotationes Zoologies Japonenscs, vol.6, part 3, p. 219, taf. 8, 3 fign. ; 1907, Zoolog. 

 Anzeiger, Bd. 32, p. 669. 



This medusa is from the fresh water of the Yang-tse-kiang River, in China, i ,000 nau- 

 tical miles from the river's mouth, near I-tschang. 10 examples were captured in April and 

 are described from preserved material by Oka. 



It is closely allied to C. sowerbii. Bell 20 mm. wide, hemispherical. Velum one-fourth 

 as wide as bell-opening. More than 256 tentacles in 7 different orders of size. The ten- 

 tacles project from the sides of the bell above the margin, the largest (perradial) tentacles 

 being the highest up. 4 elongate, oral, leaf-shaped gonads which arise from the radial-canals 

 near the stomach and project downward to the level of the velar opening. The lithocysts 

 are similar to those ot C. sowerbii. 



C. kawaii differs horn C. sowerbii in its rounded bell, larger size, and in having 7 sets of 

 tentacles instead of 3 as in C. sowerbii. The hemispherical form of its bell may, however, 

 be due to contraction, and it may be an exceptionally flourishing variety of C. sowerbii, 

 exhibiting a further growth of tentacles and attaining a larger size. This is rendered the 



