PENNARIA TIARELLA. 



187 



Pennaria tiarella McCr. 



Pennaria tiarella McCr. Gymn. Charleston Harbor, p. 51. 



Globiceps tiarella Ayres ; in Proc. Bost. Soc. Nat. Hist., p. 193, PI. X. Fips. 1 -5. 1852. 



Eucoryne elegans Lkidy. Mar. Inv. N. J. and R. I., p. 4. 1855. 



Globiceps tiarella Agass. Cont. Nat. Hist. U. S., IV. p. 344 18fi2. 



The Medusa of Globiceps fiarelln is Fip. sn. 



one of the most remarkable of our 



naked-eyed Medusa?. As in the Sarsi- 



adae, the Medusa bud is formed among 



the tentacles (Fig. 311), between the 



whirl of large and small tentacles ; the 



mode of development of the bud is 



similar to that of Coryne and Bou- 



gainvillia ; the chymiferous tubes, how- 

 ever, never have the extraordinary 



thickness which is noticed in Sarsia, 



and the cavity of the bell is hollowed 



out at an earlier period ; the Medusa bud gradually becomes very elon- 

 gated as it becomes more mature. 



Large white eggs are developed from the pro- 

 boscis, filling the whole cavity of the bell as 

 they increase in size, and giving the Medusa an 

 opaque milky appearance ; the walls of the 

 spherosome become thinner and thinner, and 

 when the Medusa bud has attained its full de- 

 velopment, and is ready to be separated, the 



walls have become so thin that the Medusae n- on 



are almost always distorted, either on one side 



or the other, by the eggs or bunches of sper- 



maries which have reached such a great size 



that four or five of them completely fill the 



inner cavity, at the same time pressing the 



sides outward, wherever one of the large eggs 



happens to be placed (e, Fig. 312) ; two or 



three of the eggs generally escape before the 



Medusa bud is liberated, and when they are 



found detached, the cavity of the bells usually 



does not contain more than one or two large 



eggs ; folds appear on the inner surface of the 



cavity of the bell after the eggs have escaped, 



Fig. 311. A fertile Hydra of Pennaria tiarella, showing the mode of budding ; magnified. 

 Fig. 312. A Medusa distended by an egg, e ; magnified. 



Fig. 313. Profile view of Medusa of Pennaria tiarella; magnified. /, folds produced by the 

 distension of spherosome. 



