Development of the Jugular Lymph Sacs. LGM 
The embryo illustrates exceedingly well the fact that, in cer- 
tain stages, or in certain individuals, while the early dorsal tribu- 
taries 1, 2 and 3 are largely taken up in the veno-lymphatic 
organization and shifted to the dorso-lateral circumference of the 
precardinal, portions of the early elements may remain as small 
and temporary channels in line with the succeeding dorsal somatic 
series, and function to a limited extent as dorsal somatic tribu- 
taries of the precardinal. 
Moreover, this embryo clearly establishes the compound 
character of the element 4, and its associated para-precardinal 
channel, and accounts for the many variations encountered in its 
connections with the main channels and its relation to the veno- 
lymphatie sac. In fact this entire question can best be discussed 
on the hand of the conditions shown by the reconstruction Just 
deseribed, compared with other typical series. 
Series 18, 7.25" Embryo 
Reconstruction of right side, 
Lateral aspect, fig. 38 and 
Reconstruction of left side, 
Lateral aspect, fig. 39 
This embryo is especially interesting for the reason that it 
illustrates very clearly the range of variation, as regards veno- 
lymphatic development, which may be presented on opposite 
sides of the same embryo. 
On the right side of the embryo (fig. 38) the straight segment 
of the precardinal receives at regular intervals three well-defined 
dorsal tributaries (1, 2 and 3 in fig. 38). In front of its confluence 
with tributary 2 the precardinal is much dilated. 
Precardinal tributary 4 of the right side is represented by two 
veno-lymphatic structures (4VL and 4VUL’, fig. 38). One is a 
triangular-shaped element(4VL’) which rests upon the dorsal 
surface of the precardinal at the promontorio-precardinal angle 
and lies in line with the precardinal tributaries 1, 2 and 3. As 
far as we are able to determine this structure does not commu- 
nicate with the venous system and may, in this case, constitute 
the anlage of the dilated, rounded appendage of the ventral divi- 
