272 George S. Huntington and Charles F. W. McClure. 
‘ardinal and promontory, which communicates with the latter at 
Tap B and at its cephalic extremity with the precardinal vein 
(Tap X). 
On comparing the caudal division of the ventral plexus in the 
10 mm. (fig. 47) and 8.5 mm. (figs. 44 and 45) embryos, it is evi- 
dent that a further confluence of the fenestra in the caudal divi- 
sion of the ventral plexus of the 8.5 mm. embryo (fig. 45) would 
produce a series of parallel and partially separated channels which 
hold the same relations to the precardinal and promontory, as do 
the three parallel channels in the 10 mm. embryo (fig. 47). It is 
also clear, considering our knowledge of the ventral plexus, in 
general, that the ventral and intermediate of the three channels 
in the 10 mm. embryo (fig. 47) must have been separated from that 
portion of the veno-lymphatic complex of tributary 4 and its 
associated para-precardinal channel, which has been contributed 
by the para-precardinal channel. , 
A comparison of the 10 mm. (fig. 47) and 7 mm. (series 138, 
figs. 33 and 35) embryos also gives us a clue, at this late stage of 
development, concerning the origin of the most dorsal of the three 
channels which compose the caudal division of the ventral veno- 
lymphatic plexus in the 10 mm. embryo (fig. 47). 
The Dorsal Division of the Veno-Lymphatic Plexus. 
This embryo is characterized by extensive development in the 
area of the dorsal division of the veno-lymphatic plexus, and by 
the complete separation of the same from the systemic veins 
except by means of its connection with the latter through the cau- 
dal division of the ventral plexus. It therefore prepares the way 
for the consideration of subsequent stages in which the entire 
veno-lymphatic plexus, as a closed and empty sac, appears to 
separate temporarily from the systemic veins. 
The possibilities of forward extension of the dorsal veno-lym- 
phatic plexus are represented here by a number of detached and 
closed sacs (VL’ in fig. 47), lying in the course of its secondary for- 
ward growth, which subsequently by fusion with it and with the 
veno-lymphatics of the cephalic division of the ventral plexus, will 
