216 George S. Huntington and Charles F. W. McClure. 
fenestration in the usual manner. The latter (4S) then enters the 
promontory as its first dorsal somatic branch. The former (4VL) 
joins the veno-lymphatic para-precardinal channel, enlarging the 
‘audal division of the ventral veno-lymphatic plexus and very 
probably forming in part or in whole the rounded appendage of the 
same noted in some of the later stages (fig. 14 and series 77, figs. 
Sl and (52): 
(b.) In another case (fig. 21, diagram), the caudal division of 
the ventral veno-lymphatic plexus joins the cephalic division and 
retains its early connections with the precardinal vein. The para- 
precardinal channel separates from the promontory at its caudal 
extremity, leaving the original point of connection with the main 
vein as a prominent conical teat or projection, lateral and close 
to the entrance of 4S into the promontory. 
It is of course evident that in an analysis of this kind it is 
practically impossible to distinguish always between clearly de- 
fined types of development and stages fixed in individual embryos 
which may or may not represent partial approximations to a single 
common genetic ground-plan. In other words, it is impossible, in 
studying any given series, to foretell the exact details of further 
development which this particular embryo would have exhibited 
if allowed to continue its course. 
On the other hand, we feel justified in establishing the above 
indicated gradations of the veno-lymphatic development by rea- 
son of the very large number of embryos which we have critically 
examined. We believe that this exhaustive study has enabled us 
to present a concise composite account of veno-lymphatic develop- 
ment to which each series subsequently described in detail can be 
correctly referred, so that the unity and consistency of the funda- 
mental plan underlying veno-lymphatic development in the cat 
becomes apparent. 
B. The Development of the Dorsal Veno-Lymphatic Plexus 
This third component of the general veno-lymphatic plexus 
is developed entirely from the main venous channels of the prom- 
ontory and posteardinal, without involving the dorsal somatic 
tributaries (5S, 6S, ete.), of this area. 
