230 George 8. Huntington and Charles F. W. McClure. 
the precardinal (fig, 24), and tributaries A-B are more dis- 
tinctly assigned to its caudal portion than in series 30. The ven- 
tral tributaries of spindle J are relatively small, but more numer- 
ous. 
Spindles J and J/ are practically confluent. Spindle JJ 
receives dorsally the well developed trunk of dorsal somatic 
tributary 1 (1, fig. 24), formed by the confluence of two branches, 
and, further caudad a secondary element, 1', belonging evidently 
to the same drainage area, and representing the branch interme- 
diate between 1 and 2 in series 30 (fig. 22). 
There is a well marked constricted interval of the precardinal 
caudad of spindle /7, between it and spindle J/J. The latter 
receives dorsally four branches, representing the drainage of the 
area assigned to dorsal tributary 2 (2 in fig. 24). 
Another elongated constricted precardinal segment intervenes 
between spindles //7 and JV. Spindle JV receives along its dorsal 
circumference six individual branches representing the drainage 
of dorsal tributary 3, in the condition of multiple small elements 
entering the precardinal separately (3 in fig. 24). 
Spindle V is occupied dorsally by the broad and complex union 
with dorsal tributary 4. This tributary is typically dilated near 
its Junction with the main precardinal vein, and contains two 
fenestral openings, which by confluence would establish the single 
space seen on the right side in embryo 30 (fig. 23) at the entrance of 
the expanded terminal of tributary 4 into the precardinal. 
Owing to imperfections in the series, the embryo was not recon- 
structed caudal to this point. In general, compared with series 
30, the embryo represents a slightly earlier developmental phase, 
marked by the larger number of individual elements composing the 
complex of dorsal tributaries 1, 2, and 3, and by the presence of 
small intermediate tributaries between the main districts. 
The general ground-plan of the embryonic venous system 
shown in the two series just considered (series 30 and 31) affords 
the most convenient approach to the detailed study of the sub- 
sequent stages in venous and veno-lymphatic development. 
Before proceeding to this study, it may be of advantage to con- 
sider briefly the steps by means of which the venous conditions in 
