HTDROZOA. 



117 



cular and radiating canals disappear, their place 

 being supplied by peculiar pouch- shaped processes, 

 communicating with the digestive cavity of the 

 polypite. 



The tentacles scarcely require any special mention. 

 Usually the distal extremities of their cavities 



Various forms of Medusidje : — a, Mqiiorea formosa, seen in 

 profile ; b, tlie same, viewed from above ; c, upper view of Willsia 

 stdlata ; d, Slabberia conica ; e, portion of the marginal canal of 

 Tiaroj^sis Pattersonii ; f, polypite of BoiigamviHea dinema ; ff, 

 part of its marginal canal ; h, Steenstrupia Owenii. (a, b and d 

 are about the natural size ; the others are magnified.) 



become more or less obliterated through vacuolation 

 of the endodermal lining. In Trachynema and its 

 allies the tentacles are stiff; not contractile, as in 

 other Mediisidw. 



I 3 



