A. M. Miller 291 
‘ 
At about the stage from which Fig. 6 was taken (5th day of incuba- 
tion) the writer found a most interesting exception to the general plan 
of development of the sub-; 
cardinal system in birds, 
which exception shows a 
striking combination of the 
conditions described bv 
Hochstetter in reptiles and 
Echidna. Anterior to the 
origin of the A. omphalomes- 
enterica and ventral to the 
aorta there is present a large 
anastomosis between the 
right and left subcardinals, 
just caudal to the point where 
the postcava joins the right 
subeardinal. Such a remark- 
able similarity to the condi- 
tions found in the earlier 
stages of reptilian develop- 
ment is certainly unusual. 
Then in addition to the usual 
anastomosis between the two 
subcardinals caudal to the A. 
omphalomesenterica there is 
also another large anasto- 
mosis about midway between 
the A. omphalomesenterica 
and the A. iliaca, which re- 
= 5 Wipe $ Fra. 6. Reconstruction of the venous system of a 
minds one very much of the chick of 5 days. Ventral view. X37. (Explanation 
state of affaits in Echidna, % rine on page 224.) 
though the fusion takes place to a less degree than in the latter. Hav- 
ing found only this one example in all the specimens examined it would 
be going too far to assert that the above ‘conditions in the chick are 
more than accidental, despite the fact that they exhibit such a striking 
resemblance to reptiles and Echidna. 
After the 5th day of incubation the subcardinals begin to decrease in 
importance, for with the gradual atrophy of the mesonephroi they have 
less and less of the function of efferent vessels to perform. The por- 
tion of each vessel caudal to the anastomosis becomes shorter; the ante- 
rior end of the left vein diminishes while the corresponding part of the 
right disappears entirely. 
