A. M. Miller 293 
organ on each side. Practically all that now remains of the subcardinal 
system is the previously described anastomosis caudal to the A. omphalo- 
mesenterica. From this time on the subcardinal portion of the postcava 
diminishes in size still more as it approaches the adult stage. In the 
adult the subcardinal system has diminished to a small part of the 
posteava just proximal to the bifurcation, including the area into which 
the genital and suprarenal veins open. 
Our attention will now be directed to the development of the genital 
and suprarenal veins which have been mentioned in the above para- 
graph. About the 5th day of incubation in the chick the suprarenal 
bodies are found lying between the aorta and the mesonephros on each 
side, dorsal to the subeardinal vein and anterior to the large anasto- 
mosis. Soon after this the sexual glands appear as elongated bodies 
situated on the median wall of the mesonephros and medial or ventral 
to the subcardinals. Both sets of organs give blood to the subcardinals. 
As has been mentioned before, the portion of the right subcardinal 
vein cranial to the point where the postcava joins the former vessel 
(cranial portion of the right subcardinal, marked ¢ in Figs. 5 and 6) 
atrophies (Fig. 6) and finally disappears (Fig. 7). So far as the writer 
has been able to determine, the suprarenal body of the right side does 
not at any period of development give branches to the cranial portion 
of the subcardinal. In Fig. 7 (sparrow, corresponding to a chick of 14 
days’ incubation) the subcardinal portion of the postcava itself les em- 
bedded in the ventral side of the suprarenal body and receives branches 
coming directly from the organ. Thus the right suprarenal vein is 
really a subcardinal derivative, inasmuch as the stem of the postcava 
is of subeardinal origin, but it is not a subcardinal derivative in the 
same sense as the left suprarenal and genital veins. 
On the left side, on the other hand, the suprarenal veins are, from 
the beginning, branches of the anterior end of the subcardinal; and as 
the anterior end of the left mesonephros gradually disappears the cor- 
responding portion of the subcardinal becomes smaller, and finally in 
the adult stage the suprarenal veins of the same side form the only 
portion that persists, and these open into the pars subcardinalis of the 
postcava. In Fig. 7 the suprarenal veins (Vv. sr. s) are seen as 
branches of the anterior end of the left subcardinal vein, and in Fig. 9 
(adult) as branches of the subcardinal portion of the postcava. The 
development of the suprarenal veins in birds, as described above, seems 
to agree with the conditions found in mammals as described by Hoch- 
stetter. 
As has been stated, the sexual glands are at first elongated bodies. 
