226 George 8. Huntington and Charles F. W. McClure. 
single tributary may become secondarily surrounded by, and 
involved in, a capillary network. We are therefore justified in 
assuming that the formation of a reticular complex in connection 
with the individual precardinal tributaries is a normal develop- 
mental character, leading up to the typical fenestral condition of 
the veno-lymphatic stage, and that its establishment may occur 
very early or be somewhat retarded. 
This view certainly coincides with the multiple arrangement 
of the first three dorsal precardinal tributaries on the left side of 
series 30 (1, 2 and 3, fig. 22), and series 31 (1, 2 and 3, fig. 24) 
which are represented on the right side of series 30 by three dis- 
tinct and single tributaries (1, 2 and 3, fig. 23). 
EARLY VENOUS STAGES. 
Series 80, 5+-""" Embryo 
Reconstruction of left side, 
Lateral aspect, fig. 22 
The cephalic or arched portion of the precardinal is moderately 
curved. The branches A—B are large and in line with the straight 
precardinal segment, entering the arch at its confluence with the 
latter. Double fenestration occurs at the junction of A—B with 
the main vein, and cephalad of the arch are several detached 
vascular islands. The proximal precardinal spindle I (I, fig. 22), 
at the posterior extremity of the cephalic arch, is only moderately 
developed. 
The first three dorsal branches of the straight segment of the 
precardinal are represented on the left side of the embryo partly 
by single vessels and partly by plexiform capillaries. Tribu- 
tary 1 (1, fig. 22) is a single vessel, which opens into the precar- 
dinal close to the terminal of tributary A—B. Tributary 2 is 
formed by three components (2, 2’ and 2”, fig. 22). 
The spindle-shaped enlargements JJ and J/J in the course of 
the straight precardinal trunk, receiving dorsally the terminals 
of 1 and 2, are, like these, closely approximated to each other. 
Dorsal tributary 3 is represented on the left side of this embryo 
by three small branches, entering the dorsal aspect of precardinal 
