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G. R. DE BEER 



(Text-fig. 11) and is hollowed out in the middle of the strand 

 (Text-fig. 12), its walls being two or more cells thick. More 

 posteriorly the cavity extends for some distance ventrally to 

 the glandular body, the latter forming its dorsal wall (Text- 

 fig. 13). It extends farther back laterally than it does in the 

 median plane. Transverse sections posterior to this region 

 show no cavity at all (Text-figs. 14 and 15). The relations of the 



Text-fig. 14. 



~PA 



-D\\/ 



Im 



m. 



I 



Petromyzon fluviatilis. Ammocoete. Transverse 

 section behind the limit of extension of the hypophysial 

 cavity showing the lateral lobes of the ' Uebergangsteil '. 



hypophysial cavity are shown in Text-fig. 16, which is a sagittal 

 section of an Ammocoete. It arises in the middle of the 

 hypophysis tissue without communication with the hypo- 

 physis depression. The glandular tissue forms its dorsal wall, 

 and at this time the pars anterior and pars intermedia, though 

 distinguishable, are in contact, being continuations the one of 

 the other in a straight line. The hypophysial cavity does not 

 separate them. Text-fig. 17 is a high-power view of this 

 stage. The distinction between the parts of the pituitary body 



