448 Development and Vascularization of the Testis 
in the illustration merely as a land mark, is densely injected but no 
attempt has been made to show its blood supply and in this and the fol- 
lowing series it appears as if uninjected. 
The Wolffian body at this time receives from ten to twelve arteries 
which richly supply the gland. In many cases a pressure sufficient to 
insure a perfect injection of the sex gland resulted in a double injection 
of the Wolffian bodies and kidneys. In the Wolffian bodies the sinusoids 
described by Minot are beautifully demonstrated in sections of five to 
twenty p in thickness. 
Allen* has noted a great activity in the formation of the primitive 
sex cells of the seminiferous tubules and of the cords of Pfliger and 
rete cords about this time, and it is posible that this increased activity 
is due to the presence of the blood stream. Allen has also shown a sex 
differentiation in the embryo of twenty-five mm. which he bases upon 
histological observations. Through a study of the vascularization, this 
sex distinction is clearly marked at 33 mm., for as Clark” has shown 
“upon the peculiarities of each circulation the differential signs of sex 
are based, a visible dorsal vessel always indicating a male; an alabaster- 
like non-vascular white cortex a female embryo.” This distinction, how- 
ever, is true more particularly of the pig and is of doubtful value in 
differentiating the human sex glands. 
In the embryo of forty-eight mm: (Fig. 2) the spermatic artery is 
found to have encircled a greater portion of the capsule of the sex gland 
and a certain amount of convolution is evident in the artery just before 
it reaches the testis. These convolutions are more marked as descent of 
the gland occurs, and this may be due in part to an attempt to shorten 
the artery. Thoma, however, in his studies of the development of the 
vascular system gives no such method of shortening. Nor, indeed, could 
this explanation account for the subsequent convolutions which occur 
after the testis has begun its descent from below the lower pole of the 
kidney. In this latter case there is a most decided lengthening accom- 
panied by more marked convolutions. A similar condition is not found 
in the human embryo, nor to such marked extent in the mouse of this 
stage. 
Microscopic sections demonstrate the capsular artery branching with 
a certain definite regularity on the surface of the gland, and sending 
minute arteries into the substance of the testis. A thick section shows 
these vessels entering perpendicularly and giving off branches which 
form capillary anastomoses around the medullary cords. 
“Clark, J. G.: The Origin, Development, and Degeneration of the Blood 
Vessels of the Human Ovary. Johns Hop. Hosp. Rept., Vol. IX. 
