72 CLAVATELLID^E. 



brane were extended into a bell, it would be converted into 

 a (so-called) medusoid ; an equally slight modification 

 would change it into an ordinary polypite. It is easy to 

 recognize in the short and wide radiating canals the basal 

 portions of the tentacles involved in the connecting web. 

 The canal, according to Krohn, runs down in the axis of 

 the arm, and penetrates each branch, reaching to its 

 extremity. 



The only additional elements besides are the circular 

 canal and the ocelli, which may be regarded as simple 

 organs of sense and the natural accompaniments of a free 

 and independent existence. 



The arms of the sexual zooid, divested of their locomo- 

 tive appendages, bear an exact resemblance to those of the 

 alimentary polypite, even exhibiting the same number of 

 opake- white patches in precisely the same positions ; in- 

 deed the general resemblance of the two, before the 

 liberation of the gonozooid, is most striking ; it is only 

 after its liberation, when it is seen striding along on its 

 stilt-like legs, the proboscis hanging down as in the swim- 

 ming forms, that the close relationship is disguised by the 

 change of posture and habit. 



The ova in this genus are produced in the extreme pos- 

 terior portion of the body, between the ectoderm and 

 endoderm (Plate XII. fig. 2, ) . The two membranes are 

 separated more and more widely as the embryos mul- 

 tiply and increase in size, and the body of the zooid be- 

 comes much distended. At last the outer wall is ruptured, 

 and the contained young are successively liberated. The 

 males are much less common than the females. 



The gonozooid of Clavatella multiplies rapidly by gem- 

 mation, the buds being developed in the interradial spaces, 

 close to the periphery of the body. Gemmation is con- 

 fined to the spring, and later on in the season gives place 

 to the production of ova, as in the common Hydra. 



