I.—PHYSIOLOGY 145 
anterior end of the gut and the brain tube. ‘The history of the pituitary 
is one of great significance, and its epithelial components make up the 
greater part of the organ in all vertebrates. 
With the development within the cranium of the epithelium of Rathke’s 
pocket the several structures which make up the pituitary body are com- 
pleted. These have been named the pars glandularis, the pars intermedia 
and the pars tuberalis; the two latter portions being developments of 
that part of the epithelium which is more particularly associated with the 
pars nervosa. The epithelial structures arise from the same source and 
show little differentiation in the early stages of growth of the organ. 
Changes in structure, no doubt associated with changes in function, occur 
later, but it is probable that even in the adult the gland possesses a reserve 
of cells from which more specialised types may arise as occasion requires. 
Although the division of the pituitary body into components, showing 
different structural characteristics, is the rule in mammals, great variations 
in their relative amounts occur in different species and also in individual 
animals of the same species. The pars glandularis is the predominant 
feature in all vertebrates; the pars intermedia, pars tuberalis and pars 
nervosa are much more variable. The close connection between the 
epithelial derivatives and the diencephalon is always found. 
The pars glandularis or anterior lobe of the mammalian pituitary con- 
tains three distinctive kinds of cell, differing in their relative proportions 
and positions in different animals. The chief element is the chromo- 
phobe or mother-cell. It closely resembles the type of cell characteristic 
of the pars intermedia, though whether the two are identical in structure 
and function cannot be stated. ‘These cells appear to be the least differ- 
entiated of the elements arising from Rathke’s pocket, and evidence 
poirits to their being able to undergo further development with the forma- 
tion of the two other types met with in the lobe, acidophil and basophil 
cells. Severinghaus states that Golgi bodies appear in the chromophobe 
cells of two kinds, filamentous networks and perinuclear rings. The 
nature of the Golgi body indicates the type of cell which is in process of 
development; the cells possessing the network become acidophil, and 
the ringed cells form the basophil element. The chromophobe cells 
are the most abundant, but it is as yet undetermined whether they are 
functionally active as such, or are merely reserves from which the secre- 
tory elements are subsequently formed. In the human pituitary body 
Rasmussen estimates the chromophobe cells at 52 per cent. of the total, 
the acidophil at 37, and the basophil cells at 11 per cent. Variations in 
their relative numbers have been described in different physiological 
conditions. Charriper and Hatterius state that in the female rat the 
basophil cells predominate during oestrus, and the eosinophil cells during 
the interval. Modifications of the cells have been described as occurring 
in pregnancy, after castration, and in other conditions. ‘The histological 
picture can be very varied, and can be rapidly changed. 
MopeE OF SECRETION. 
In all vertebrates the epithelial lobe is characterised by extreme vascu- 
larity. In elasmobranch fishes the arrangement of its cells in acinar 
