tN 
ZOOLOGY 
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edge of the umbrella, and the radial canals, which communicate 
with the cavity of the oral cone on the one hand and the 
circular canal on the other. On the aboral surface of the 
endodermal lamella the middle layer usually becomes much 
Ws 
WY 
Fic. 39. a 
thickened, its gelatinous substance may remain structureless, 
or cells may invade it. 
Tubularia is one of those Hydromedusae which do not 
give rise to free medusae. The medusa is produced, but does 
not break away, it remains connected with the hydranth by 
the aboral pole. Ina mature individual a racemose extension 
of the body-wall is formed between the two rows of tentacles. 
