214 FREDERICK TILNEY 
tissue. To the collection of ganglionic cells situated at the 
upper end of this duct he attributes a function similar to that 
of the osphradial organ in mollusca, thus bringing it into general 
relation with the olfactory apparatus. It is also his opinion 
that the hypophysis, in this sense, was functionally active in 
the ancestral vertebrates and that while the bucco-neural duct, 
has been obliterated the sub-neural or pituitary gland with the 
collection of ganglionic cells has persisted. Ayers (2) is in ac- 
cord with this theory when he states that the hypophysis arose 
as an organ of taste and the infundibulum was its nerve. Further . 
evidence of this kind is furnished by Ganin (3), who was among 
the first to observe a connection between the anterior extremity 
of the embryonic neural tube and the branchial cavity in Ascid- 
ians. Similar observations were made upon chordata by Kowa- 
levsky (4), Ussow (5), Julin (6) and von Kuppfer (7); the latter 
expressing himself as follows: ‘‘Der Verbindungskanal zwischen 
Hirn und Darm schlage ich vor als Canalis Neurentericus an- 
terior zu bezeichen und die Glande hypophysaire von van 
Beneden und Julin wire wohl am einfachsten als Neural-driise 
zu benennen.”’ 
It seems probable in the light of these observations that such 
variations as do appear in the floor of the interbrain of craniates 
are adaptive in their nature. This idea is borne out by the fact 
that of ‘all the structures arising from the diencephalic floor- 
plate the infundibular process is the most variable. This proc- 
ess from its early phases of development in all forms maintains 
close relation to the stomadaeum, pituitary evagination and 
branchial cavity. As an adult structure its modifications are 
numerous. 
In the selachian (Mustelus laevis; fig. 1, A) the processus 
infundibuli projects caudad from the floor of the third ventricle; 
it presents two surfaces, i.e., a ventral or pituitary surface in con- | 
tact with the pituitary gland, and a dorsal or saccular surface 
which is much convoluted and highly vascular forming the 
saccus vasculosus. In the amphibian (Rana pipiens; fig. 1, B) 
the same general relations obtain and the two characteristic 
surfaces are present except that the dorsal or saccular surface 
