1 4- Papers from the Marine Biological Laboratory at Tortugas. 



which while at rest were extended radially in a circle four or sometimes 

 five times as wide as the bell, are shortened to half their extreme length. 

 A succession of rapid, jerky contractions of the bell drives it forward for 

 a short distance. It then settles slowly down until something solid is 

 reached, when it either fastens itself for a short rest, or starts off at once 

 on another voyage. The bell changes in shape by about one-fourth of its 

 diameter at each contraction. The main part of the tentacles seem to be 

 rather a hindrance than a help in locomotion. They are held stiffly out at 

 less of an angle than when fixed to some solid object. With the slender 

 terminal processes, they extend backward in the water and probably assist 

 the swimming movements to the extent of steadying them somewhat. 



In case the jelly-fish chanced to be hanging suspended by one or two 

 tentacles from a bit of seaweed when the swimming commenced, it seemed 

 to possess no means of knowing that it was not in the proper position. 

 The course of the swimming was never seen to be changed from downward 

 or sidewise to upward. From the horizontal position, as when resting upon 

 the bottom, the dozen or so of impulses given to the bell before stopping 

 usually sufficed to drive it upward to the surface, or near to it, in a fairly 

 regular fashion, and with moderate directness. But the sidewise or down- 

 ward course was much more erratic, the little creature bobbing first this way, 

 then that, in tipsy style. The fact that the center of gravity is, as will be 

 noted later, so low down on the bell is probably the occasion of this difficulty 

 in maintaining a straight course when the bell is in any other position than 

 the normal one, right side up. A number of counts were made to find the 

 rate of the swimming contractions, and it was found that at the average tem- 

 perature of the water in the moat during the summer the pulsations of the 

 bell averaged a rate of 200 per minute, the activity being continued for only 

 a few seconds. The jelly-fish appeared to become fatigued after from ten 

 to twenty pulsations. 



' Fishing " reactions. As in the case of the famous fishing medusa of 

 Woods Hole, Gonionemus, each period of active swimming is succeeded by 

 a period of passive floating in the water, the outspread tentacles ready to 

 seize any prey that might chance to come in the way. As soon as the pul- 

 sations cease, the tentacles stretch out into the water and are swept upward 

 over the top of the bell by its downward course. At this time the position 

 is similar to that shown by Allman 1 as the typical resting attitude of '" C. 

 radiatmi! " (now known as C. alhnani}. This "hands-up" posture is, I 

 believe, never taken during periods of rest by the species under discussion. 



Resting attitude. Cladoueina comes to rest margin down, instead of 

 inverted as in the case of Gonioneinus. The suctorial appendages apply 

 themselves to the bottom the instant the medusa touches. There are from 

 two to five of these on each of the nine tentacles, arising from the lower or 

 axial surface of the tip end. These processes are smooth, devoid of nema- 



Allman. 1871. Monograph of the Gymnoblastic Hydroids, plate xvir, fig. 4. 



