102 



HALOPSIS CRUCIATA. 



more a Eucope. This may eventually show us two modes of develop- 

 ment among the JEquoridae into forms, forming groups corresponding to 

 those of the OceanidoB and Eucopidse as here limited, in one of which 

 the young Medusa has a deep bell and few tentacles, as in Clytia and 

 Oceania, while in the other group they have, when hatched from the 

 reproductive calycles, a flat disk and many tentacles, as in Eucope and 

 Obelia. 



Massachusetts Bay, Nahant (A. Agassiz). 



Cat. No. 364, Nahant, August, 1862, A. Agassiz. Medusa. 



Cat. No. 375, Nahant, 1863, A. Agassiz. Medusa. 



Halopsis cruciata A. AGASS. 



During the early part of the summer there is frequently found a 

 Medusa, at first supposed to be the young of Halopsis oceUata ; a com- 

 parison of the size, the character of the genital organs, and the number 



of tentacles, shows this to be im- 

 possible. If. cruciata never grows 

 to more than one and a half to two 

 inches in diameter. The tentacles 

 are much less numerous (Fig. 151), 

 the genital organs are lobed pouch- 

 es, hanging down in folds from the 

 chymiferous tubes ; there are only 

 three compound eyes between ev- 

 ery two of the chymiferous tubes ; 

 these three eyes are already pres- 

 ent in the youngest Medusa3 ob- 

 served, which measure hardly half an inch in diameter, and in which 

 the genital organs are already well developed, while in the young of 

 If. ocellata, in specimens measuring nearly two inches, and having as 

 many as twelve chymiferous tubes, we find no trace of them. The bell 



of these young Medusae is very high ; the eyes 

 differ from those of If. oceUata, having only four 

 or five granules arranged in a single row ; the 

 tentacular cirri and the large tentacles are essen- 

 tially the same in both species ; the spermaries 

 of the males are quite slender and more linear, 

 compared to the heavily filled, convoluted genital 

 pouches of the females. The genital organs are 

 of a light pink color, as well as the bell. 



Fig. 151. A profile view, somewhat magnified, of Halopsis erucia 

 Fig. 152. A natural attitude of the same species ; both females. 



