52 



PE TROM YZONTIA 



remarkable features bridge over the gulf between the Craniata 

 and the Cephalochorda. 



The mouth is bounded by lips (Fig. 37) ; there is neither sucker 



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nor horny armature, nor yet any rasping 'tongue.' The buccal 

 cavity is separated by a velum from the pharynx, and this is limited 

 in front by an encircling ciliated groove (like that of Amphioxus), 

 which is at the level formerly occupied by the transitory first gill- 



