208 ROBERT PAYNE BIGELOW ON 



The oral arms and their branches are usually spread out so as to cover the sub- 

 umbrella completely, but they are almost always in motion, bending to one side or the 

 other, and they may be flexed aborally until the tips come within the umbrellar 

 margin, or extended until they reach far beyond. Besides these general movements, 

 the various appendages of the oral arms have movements of their own. Muscular con- 

 tractions may be observed also in the thin membrane that separates the stomach from 

 the subgenital cavities, and they probably serve to renew the water that bathes the 

 gonads. 



When the oral disc has been severed from the umbrella, both parts may remain 

 alive for several days, and both retain their powers of spontaneous movement. The first 

 effect of the operation is often to throw all of the parts into a strong tetanus, but shortly 

 afterwards the pulsations of the umbrella may be renewed at a rate considerably more 

 rapid than normal, — 32 to 34 per minute in one case. When the medusae have been 

 for some time under unfavorable conditions, it frequently happens that the part of the 

 body-wall surrounding the periphery of the stomach is ruptured, and thus the mouth parts 

 as a whole become separated automatically from the umbrella.^ 



While at Bimini, Bahamas, in 1892, I observed that the food of Polyclonia frondosa 

 consists chiefly of copepods and other small Crustacea, and that these are caught by the 

 combined action of the oral vesicles and the oscula ('93, \>. 106). If a copepod strikes 

 a vesicle, the vesicle bends quickly so as to cover the mouth of the adjoining oscu- 

 lum, and the copepod is thus enclosed in a trap. Artificial stimulation would cause the 

 same reaction. 



Experiments on Cassiopea xamachana made to determine whether or not this 

 species obtains its food in the same way gave negative results. Stimulation of an oral 

 vesicle causes only a slight bending on the side stimulated. Although these vesicles are 

 provided with batteries of nettle cells near the tip, I was unable to see that they played 

 any part in the taking of food. It may be that they are protective, but the sting is 

 very feeble. 



Examinations of the contents of the stomach were almost equally unsatisfactory. 

 The contents of twenty-two stomachs were examined, and of these fourteen contained 

 only a clear, very viscous fluid and, in some cases, a few apparently ripe eggs, more or 

 less distorted, some small, colorless cells, probably sloughed off from the endodermal 

 epithelium, and green cells identical with the " zoanthelae '' found in the mesogloea. One 

 or more copepods and other Crustacea were found in five specimens. In one of these one 

 small amphipod was found, and in another the cornea of an unknown crustacean. 



' While tliis paper is passing through the press a paper has appeared by E. W. Berger (1900), in which lie gives the 

 results of experiments made by F. S. Conaut upon Polyclonia and Cassiopea to test the effect of removing the rhopalia. 



