242 George 8. Huntington and Charles F. W. McClure. 
arch and straight portion of the preeardinal. The precardinal 
receives dorsal somatic tributaries 1, 2, 3 and 4. 
Several detached vascular islands, notably between A-B and 
tributary 2 are present. The para-precardinal channel has been 
separated from the main precardinal vein independently of tribu- 
tary 4, or, if at one time connected with it, this connection has 
been lost. In other words, the embryo under discussion is one of 
the instances illustrating the type of development described in 
the analysis (cf. p. 215, fig. 19), in which the caudal division of the 
ventral veno-lymphatic plexus is apparently derived entirely 
from the para-precardinal channel, without involving tributary 4. 
In the present instance, the elongated fenestra Y in fig. 31, 
between the precardinal and promontorial terminals of the para- 
precardinal channel, is replaced on the left side of the embryo 
by two rectangular foramina (fig. 32, Y’ and Z); consequently the 
para-precardinal channel here drains through the resulting inter- 
fenestral pathways, by three separate and distinct openings into 
the main channel. 
The fenestral character of the terminal of tributary 4 (4, fig. 32), 
indicates that a secondary channel is being formed along the pre- 
cardinal vein, independently of the para-precardinal channel, by 
means of which tributary 4 will subsequently drain into the 
promontory. 
The dorsal veno-lymphatic plexus is more advanced in develop- 
ment on the left side than on the right. It is continuous cephalad 
with the caudal division of the ventral veno-lymphatic plexus, 
and caudad with the anlage common to the primitive ulnar vein 
and the primitive ulnar veno-lymphatic. This anlage has differ- 
entiated completely from the postcardinal vein, caudal to the 
termination in the latter of dorsal somatic tributary 7 (fig. 32, 7S). 
The anlage of the permanent external jugular system is represented 
on the left side by a single trunk (fig. 32), corresponding to the 
double vessel found on the right side (fig. 31) in the same situation. 
Compared with the preceding series (109, 6.2mm., figs. 27 and 
29), the right side of this embryo (fig. 31) shows retarded develop- 
ment of the dorsal veno-lymphatic plexus. A single channel, 
closely following the dorso-lateral circumference of the promon- 
