456 Development and Vascularization of the Testis 
which the capillaries encircle the tubules. In Fig. 11 are seen the 
capillaries, some larger arteries and a portion of one of the large as- 
cending perpendicular branches given off shortly after the looping of 
the descending perpendicular branch near the center of the gland. The 
tubules of the pig testis show this capillary arrangement somewhat better 
than do those of the human adult male sex gland, for as was shown by 
Krause the tubules of the human testis measure two-tenths of a mm. in 
diameter, while I find that the tubules of the sex gland of the pig are 
between two-tenths and three-tenths mm. in diameter. 
Fig. 12. Corrosion specimen of the testis of an adult pig, showing the 
typical arterial loops. X 2. 
The various types of arterial loops comprising the descending perpen- 
dicular artery and its ascending branches are shown in Fig, 12. These 
loops were taken from corrosion specimens of the adult testis of the pig. 
In the figure they are arranged in order of frequency, the last having 
a recurrent branch before the abrupt looping, being very rare. No simi- 
lar arrangement was found from studies of corrosions of the human 
gland. 
What the causes are which produce this peculiar arrangement it is 
difficult to say. In the first five figures representing early embryonic 
stages the arteries were found to penetrate the gland perpendicularly 
but to give off branches as they descended. 
This is depicted in Fig. 13. 
