138 



TEXTBOOK OF ZOOLOGY 



of the bell. Tentacles are usually present also on the margin of 

 the bell. This is the most numerous and extensively distributed 

 group of Scyphozoa. Aurellia and Stomolophus are common examples. 

 Aurellia* is the typical example, and, like most jellyfishes, is 

 composed largely of water. When they are dried, only a thin film 

 remains. This is a common one and ranges from New England to 

 the Gulf of Mexico. It may reach a foot in diameter. 



Cut surface of body wall 



Stomach 



Qonad 



^ Jub-gsnital pit 



Upper portion of 



manubrium 



-^r — Lateral mouth 

 \ Radial canal 



- -Sub-umbrella 

 space 



— Grtutor 

 muscle 



Manubrium 

 (cut surface) 



Central mouth 

 Oral tentacles 



Fig. 62.- 



-Cabbage-head jellyfish, Stomolophus meleagris, a very common form in 

 the Gulf of Mexico. Bisected to show internal structure. 



The animal has no velum as do the hydromedusae, but there is 

 a square mouth on the subumbrellar side with wing-shaped, liplike 

 oral lohes or arms. A suhgenital pit lies in each quadrant of this 

 side of the animal. The mouth leads through a short passageway 

 into the angular gastrovascular cavity which in turn has four lateral 

 gastric pouches containing the fringelike gonads. There is also a 

 row of small gastric filaments here carrying nematocysts. A large 

 number of branching radial canals extend from the gastrovascular 

 cavity out to the margin of the bell, there joining a circumferential 



•This spelling is according to Mayer's monograph, 

 proposed by Peronas Le Sueur was so spelled. 



The generic name flrst 



