STUDIES ON*GANOID-FISHES| 
Il. THe DEVELOPMENT OF THE HYPpopHysiIs OF AMIA. 
JacoB REIGHARD AND S. O: Mast. 
In describing the origin and early development of the 
hypophysis it is convenient to refer to definite stages in the 
development of Amia, as designated in the preceding article 
on “The Development of the Adhesive Organ and Head Meso- 
blast of Amia.”’ 
By referring to Fig. I accompanying the article just 
mentioned it will be noticed that there is a slight depression 
between the anterior end of the neural tube and the adhesive 
organ. This depression marks the position of the fundament 
of the hypophysis. A median longitudinal section (Fig. 1) 
through an embryo of this stage, shows the ectoblast to con- 
sist of two layers. The outer layer is thin and quite uniform 
in thickness. It is composed of a single tier of rounded 
opaque cells which are slightly flattened. The inner layer, 
also composed of a single tier of cells, approximately cubical 
in form, is about as thin as the outer except over a consider- 
able area in the region dorsal to the anterior end of the neural 
tube, where it gradually becomes thicker from all sides, ex- 
tends inward and becomes continuous with the walls of the 
neural tube which at this point extend outward forming a 
small funnel-shaped evagination in the dorso-anterior region 
of the neural tube, or forebrain. A similar evagination is 
designated lobus olfactorius impar by von Kupffer (1893) 
in Acipenser. In the following description we shall, following 
Haller (1897), speak of the tissues (Fig. 1, np.) between the 
‘From the Zodlogical Laboratory of the University of Michigan, Ann 
Arbor, Michigan, U. S. A. 
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