342 H. B. POLLARD. 



Mouth and Hypophysis. 



The mouth and hypophysis in Teleostei formed the subject 

 of Dohrn's first two studies on the ancestral history of the Ver- 

 tebrate body. He stated that the mouth appeared first as a pair 

 of lateral openings of the alimentary canal to the exterior, and 

 that the hypophysis arose as a bilateral outgrowth of the upper 

 wall of the alimentary canal in front of the endodermal pouches 

 which form the mouth. 



This account was criticised by Hoffmann (10), who described 

 the hypophysis as developing from a thickening of the lower 

 layer of the ectoderm in front of the mouth opening — that, in 

 fact, in Teleostei, just as in other Craniata, the pituitary body 

 is an organ derived from the epiblast of the stomodseum. 

 Subsequently Dohrn, in his fourth '' study," modified his first 

 views to the effect that there exists an ingrowth of ectoderm. 

 I find that Professor Dohrn's figures are correct, except as 

 far as the interpretation of the endoderm is concerned. Exa- 

 mination of earlier stages gives the true explanation. With 

 HoflFmann's figures and statements my own conclusions on 

 Gobius do not agree, though from individual pictures by 

 Henneguy (6) and Goronowitsch (4) the development in Salmo 

 appears to be the same as in Gobius. 



Dohrn's account was confirmed by Miss Piatt (18) for 

 Batrachus tau. On the other hand, all doubleness of origin 

 of the mouth is denied by Mcintosh and Prince (16) for pelagic 

 Teleostei. Nor, according to the same authors, is a stomodaeum 

 or involution of epiblast present. 



Figs. 6 — 10 represent sections through the mouth and hypo- 

 physis regions of my first stage of Gobius capito embryos. 

 Fig. 2 gives a diagrammatic view of the general relations. 



Examining first fig. 9, whose position is indicated on the 

 diagram by the line d — d, it is seen that the section is some- 

 what oblique, cutting the eye on the left near its posterior edge, 

 and on the right nearer the centre of the lens. In the middle the 

 brain is cut in section between the mid- and fore-brain, where 

 it is most compressed from side to side. Below the eye, on 



