284 G. R. DE BEER 



Stendell (1914a) makes no mention of Amia, and remarks 

 that the Ganoids are in need of much further study in this 

 respect. In view of the diversity of opinion on this matter and 

 the fact that the confirmation of either of these two theories 

 must lead to important conclusions with regard to the hypo- 

 physis, I determined to examine my preparations of embryonic 

 and larval stages of Amia. 



The material consisted of sets of serial sections, sagittal, 

 horizontal, and transverse ; and I may say at once that the 

 remarks made by Eeighard and Mast with regard to the care 

 necessary in making the preparations are well founded. By 

 shrinking of the egg-membrane the contained embryo is often 

 compressed and the limits of its organs are sometimes difficult 

 to make out with certainty. Thionin was found to be an 

 efficient stain although it unfortunately fades. For bringing 

 out the basement membranes Lichtgrlin or acid fuchsin were 

 found to be useful as counter-stains after safranin and methylene 

 blue. 



The Origin of the Hypophysis. 



The earliest stage in which the hypophysis was visible is 

 shown in sagittal section in Text -fig. 26. The brain is in contact 

 with the antero-dorsal ectoderm in the region where the neuro- 

 pore has closed. The antero-ventral region of the head is 

 occupied by a mass of large endoderm cells containing abundant 

 yolk and destined to form the adhesive organ. Between the 

 latter and the brain is a tract of smaller cells almost devoid of 

 yolk-granules, in contact with the ectoderm antero-dorsally, 

 and postero-ventrally tapering into a point where the brain 

 comes into contact with the endodermal roof of the fore-gut. 

 There can be no doubt that these cells originate from the 

 ectoderm. 



The next stage is shown in small scale in Text-fig. 27 and under 

 higher magnification in Text-fig. 28. The tract of ectodermal 

 cells described in the previous figure is more compressed and 

 denser. Anteriorly it shows traces of previous connexion with 

 the inner layer of superficial ectoderm of the front of the head. 



