20 The Paraphysis in the Common Fowl 
central cavity of the gland into its walls are in this section plainly 
visible. 
It seems to me that Minot’s (9) supposition regarding the paraphysis 
in amphibia and birds is a perfectly correct one. It is inconceivable 
that the paraphysis can for a moment be thought of as an organ of 
sense. It is much more probable that it is an appendix of the para- 
physal arch, developed from the brain wall, and, as we have seen, its 
outermost layer in the adult is composed of a modified ectodermic tissue. 
In the younger stages its walls are thin and its cavity is large, but in 
the adult chicken or hen the reverse is true. A narrow, cleft-like 
cavity persists, surrounded by moderately thick walls. The gland is 
oval in shape and is not far 
from 150 y in its greatest 
diameter, which lies nearly 
parallel with the longitud- 
inal axis of the cavity of 
the forebrain. It is an ab- 
solutely constant structure, 
and I have been able to 
identify it time and time 
again in the embryo, in the 
chicken, and finally in the 
full-grown fowl. Its posi- 
tion is very characteristic. 
The paraphysis is situated 
PCO DEO: 
Fria. 8A. Paraphysis of a 10 days’ chicken. Sagittal immediately dorsad to the 
corre. BB Wesicle of a8days’ chicken. Frontal sec- foramen of Munro, and an- 
Meta tne terior to a prominent fold 
of the choroid plexus which must morphologically correspond to the 
velum transversum. 
Fig. 8B is a section of a portion of the pecuhar vesicle above re- 
ferred to shown under a high power. The preparation is from the 
same series as Fig. 7 but a different section, a little farther dorsad to it 
was chosen, as the cells seemed to show more distinctly than those 
in the previous section. The wall of the vesicle is granular in struc- 
ture, with large round nuclei, which in each case contain a small, irregu- 
larly-shaped nucleolus. At times the nucleolus appears as a round dot, 
or presents a linear appearance. It may represent quite a regular cross, 
or even be star-like in shape. Externally there is a layer of mesenchy- 
mal tissue, and internally what presents the appearance of a distinct 
membrane. Within the cavity of the vesicle, there is almost invariably 
