188 



PENNARIA TIARELLA. 



owing to their distension (/, Fig. 313) ; as soon as the eggs have all 

 escaped, and the Medusae have become detached, they move about with 

 great activity, their motions resembling the quick, restless movements 

 of Sarsia, 



The size of the free Medusa is about one sixteenth of an inch ; the 

 walls of the spherosome are so thin that the Medusa will often assume 

 a quadrangular or octagonal outline (Fig. 314), with deep indentations 

 between the chymiferous tubes (Fig. 315); the digestive trunk is short, 

 bottle-shaped, not extending more than half the length of the inner 

 cavity of the bell; it is suspended by the narrow part (Fig. 313), the 

 connection of the digestive cavity with the Hydrarium dividing the 

 abactinal part of the bell in such a way that when seen in profile there 

 are two circular masses above the chymiferous tubes. As the Medusa 

 grows older, this open connection does not seem to diminish, as it does 

 in the Sarsiadae, Bougainvilleae, and others. The chymiferous tubes, 



Fi-. 314. 



four in number, are broad, running almost perpendicularly, after mak- 

 ing a sharp bend at the top, from the abactinal pole to the circular 

 tube ; there are also four well-developed sensitive bulbs ; the tentacles 

 on the contrary remain always in a rudimentary condition (Fig. 313), 

 being simply four small knobs scarcely projecting beyond the general 

 outline of the bell ; the opening of the veil is small. 



What becomes of the Medusa after the eggs have escaped, I am not 

 able to say, though I am inclined to think that they do not undergo 

 changes of any importance, as I have kept them in confinement for 

 three weeks without noticing any striking differences. The color of 

 the Medusa, when freed from its eggs, is of the most delicate rose color; 

 the digestive trunk and the chymiferous tubes are a little darker, and a 

 line of rich crimson pigment-cells, running almost their whole length, 

 makes this Medusa one of the most brilliantly colored of our coast. 

 Found at Naushon, during the month of September. 



Buzzard's Bay (Ay res, A. Agassiz) ; Massachusetts Bay (A. Agassiz) ; 

 New Jersey (Leidy) ; Charleston, S. C. (McCrady). 



Fig. 314. A different attitude of the Medusa, seen from the actinal pole. 

 Fig. 315. Fig. 313, seen from the abactinal pole. 



