224 George 8. Huntington and Charles F. W. McClure. 
interpretation is, however, based on a vastly larger number of 
embryos than those figured in this paper. Each of the series 
quoted in our list of material has been carefully and completely 
examined by one or both of the authors, and many reconstruc- 
tions have been made in addition to those here published. We 
consequently feel that the tentative value given by us to the indi- 
vidual developmental components of the jugular lymph sacin the 
embryos of the cat is based on sufficiently extensive observation 
and comparison, and that we are warranted in offering an onto- 
genetic history of the jugular lymph sae in which definite embry- 
onic stages follow each other with remarkable uniformity in the 
entire series and Jead uninterruptedly to the conditions established 
in the adult. 
On account of the very narrow limits of the venous system 
within which the development of the jugular lymph sacs is con- 
fined, it was found advantageous, in reconstructing certain stages, 
to elongate the reconstruction by using thicker wax plates than 
the #-measurement and magnification of the sections actually 
called for. This was done with the purpose of separating, and 
thus more easily determining, the arrangement and position of the 
complex of veno-lymphatic components of the jugular sacs. 
With these few exceptions, all of the reconstructions shown in 
this paper have been reconstructed and drawn to scale. The few 
that have not, however, illustrate equally well the main princi- 
ples of veno-lymphatic development, but appear slightly more 
elongated than the actual dimensions call for. 
In the early stages the precardinal vein is, in conformity with 
the more elongated form of the embryo, less curved in its anterior 
or arched segment than in the later stages, and less distinctly 
divided into the typical districts shown in the composite scheme 
(fig. 8). The caudal or straight portion of the precardinal is 
somewhat elongated, and presents, at more or less regular inter- 
vals, oval or spindle-shaped enlargements (series 30 and 31, figs. 22 
to 24), which correspond to the confluence of ventral and dorsal 
tributaries with the main channel. These enlargements of the 
precardinal are evanescent and are evidently produced by the 
increased amount of blood entering the main vein at these points 
