494 MURBACH. [Vol. XI. 



their nettling organs). He gives the actinal diameter as -^-^ of 

 an inch. 



The medusae remain rather quiet during the day unless dis- 

 turbed, but become very active as darkness sets in. 



Largest specimens taken were 3 cm, in diameter, and had 

 64 tentacles; the smallest were 6 mm. in diameter, and had 32 

 tentacles. 



Each tentacle is bent near the end on account of a pad of 

 cement cells on the oral side, by means of which the animal 

 fastens itself to foreign objects. It does not use its nettling 

 organs for this purpose, as Agassiz supposed. 



The color varies from deep brown or orange to paler shades, 

 except the chymiferous tubes, which are always dark. The 

 tips of the tentacle frequently are a deep pink. 



These medusae are said to have occurred here last year in 

 small numbers in the Eel Pond, a small body of water contain- 

 ing about five acres, with only one outlet into the Harbor. 

 This year as many as two hundred were taken in one evening 

 with the tow-net. They were so much sought after as speci- 

 mens that it is now difficult to find enough for completing the 

 work. 



When seen from the aboral side in the water they are at 

 once conspicuous by the cross formed by their gonads, by the 

 bright green pigment-spot at the base of the tentacles, and by 

 the radiating brown tentacles. 



The females are usually darker than the males. This may 

 be due to an abundance of ripe eggs on the periphery of the 

 ovarian folds. The pigment to which the general color of the 

 gonads is due lies in the deeper portion of the gonads. 



Eggs and sperm are dehisced from the outside of the gonads 

 by the breaking up of the epithelium. 



Dehiscence occurs normally about one hour after twilight — 

 about 8 o'clock at this season of the year. Repeated experi- 

 ments show that it is dependent on the withdrawal of light, 

 since medusae taken at any time of the day, when placed in 

 the dark for about an hour, deposited sperm and eggs.^ 



1 Brooks (in " The Life-History of Hydromedusae," Mem. of the Boston Sac. 

 of Nat. History, vol. Ill, No. 12) is inclined to think that marine animals deposit 



