DEVELOPMENT OF THE HYPOPHYSIS 431 
spaces may be due to shrinkage, as has been suggested in the case 
of the colloid in the thyreoid follicles. In all respects it is similar 
to that found in the anterior lobe. There is no direct outlet by 
means of which a secretion can reach the cavity of the vascular 
sac and thus gain entrance to the ventricles of the brain. The 
absence of any secretion in the vascular sac also argues against 
there being a pathway for the secretion to enter it. It would 
seem probable that another secretion, distinct from this, is formed 
in the lumen of the tubules. As stated in the description of the 
histology of the adult hypophysis, the granular cytoplasm is 
always found on the peripheral side of the cell cords or tubules 
and never on the side toward the lumen. It is probable that 
this secretion finds its way into the numerous capillaries along 
the periphery. In the formation of two secretions, therefore, the 
hypophysis resembles the thyreoid in some forms, and also the 
hypophysis in some mammals. 
2. Histogenesis of the hypophysis 
In 7.5 mm. embryos the walls are formed of a single layer of 
cells of a large cuboidal type. The cytoplasm is slightly granular 
and somewhat acidophilic. The nuclei are large, somewhat 
oval, placed near the basement membrane, and contain con- 
siderable chromatin network. Usually several nucleoli, although 
sometimes only one, are found near the nuclear membrane 
(fig. 31). Very soon the walls of the hypophysis are composed 
of several layers of cells. Ina13 mm. embryo the large nucleoli 
are no longer so prominent and, as a rule, only smaller pseu- 
donucleoli, as observed by Sterzi, are to be seen. 
a. Anterior lobe. Ina 21mm. embryo, very little of the floor 
of the anterior lobe is as yet present. The walls are composed 
of two layers of columnar cells which have a thin outer and a 
thick inner, slightly granular cytoplasmic zone. The large 
and elongately oval nuclei contain a dense chromatin network, 
especially in the anterior end (fig. 32). Sterzi has observed 
that there are some elongated nuclei in the roof of the hypophysis 
in which the long axes are at right angles to the surfaces, and 
