214 George 8. Huntington and Charles lk’. W. McClure. 
remains intact as the first somatic promontorial 
tributary and does not participate in veno-lymphatic 
development. 
The two main genetic types observed by us in the development 
of the caudal division of the ventral veno-lymphatiec plexus, in 
embryos between 7 and 10 mm., may be presented schematically 
in the series of diagrams figs. 8 to 14 (lateral views, left side) and 
in figs. 11A, 18 and 19 (dorsal views). 
1. Deriviation from para-precardinal channel and veno-lym- 
phatic component of precardinal tributary 4. 
Early Venous Stage (fig. 8). 
Tributary 4 of the precardinal series is marked by its large size 
and extensive area of drainage, and by its expanded plexiform 
terminal. 
Intermediate Stage. 
The beginning of veno-lymphatic organization in general is indi- 
cated along the line of the primary dorsal precardinal tributaries 
by expansion and reticular fenestration of their terminals. In 
the area controlled by precardinal tributary 4, the precardinal 
begins to differentiate along its dorsal circumference a sec- 
ondary para-precardinal channel (figs. 9 and 10). 
Early Veno-lymphatic Stage. 
The precardinal tributaries, in general, have begun to separate 
into dorso-medial somatic (1S, 2S, 3S, and 4S), and dorso-lateral 
veno-lymphatic components (1VL, 2VL, 3VL, and 4VL, in figs. 
11, 11A and 18). 
The para-precardinal channel, having, for the most part, 
assumed the function of draining the territory formerly controlled 
by the primary precardinal terminal of tributary 4 (fig. 8), has 
become associated with the veno-lymphatic component of 4 (4VL), 
which in turn is in process of multiple fenestral separation from 
the somatic element of 4 (4S). Cf. fig. 114 which is a dorsal view 
of fig. 11 in the region of the promontorio-precardinal angle and 
fig. 18, alsoa dorsal view, which shows this process of separation ata 
more advanced stage of development. — 
