CTENOPHORA 



147 



now be called, exhibit a tendency to orient themselves 

 radially about the central cavity d. Designating the point 

 of transition of the fundament of the stomach into that of 

 the infundibulum as the inner opening of the oesopTiagus or 

 infundibular fissure, the increase in the length of the stomach 

 causes this fissure to move into the central cavity, a w^all 

 being formed by means of which a central portion of the 

 cavity is separated from a lateral part (Fig. 68). This 

 lateral portion is not retained as a single space, but divides 

 into four diverticula, which, in accordance with their mode 



Fi&. 69.— Further formation of the gastrovascular system after Chun). A, 

 embryo of Beroe, in optical transverse section at the time of formation of the four 

 entodermal sacs ; ek, ectoderm ; en, entoderm ; g, mesogloea. B, development of 

 the permanent canal system in an embryo of Eucharis muUicornis. View from 

 below: m, stomach ; mg, fundament of the gastral vessels; x, fundament of the 

 meridional vessels ; r, ciliary plates ; i/, fundament of the tentacular vessels ; ih 

 tentacle base [Tentakelhodcn} ; ts, tentacle stalk ; t, tentacle. 



of origin, communicate at their upper parts with the central 

 infundibular fundament, and have their blind ends directed 

 orally (Fig. 68 d and Fig. 69 A). Inasmuch as the greater 

 portion of the entodermal cells is grouped about these four 

 blind sacs, it is divided from now on into the four so-called 



