186 George 5. Huntington and Charles F. W. McClure. 
In a 15mm. cat embryo he observed that 
in one section (266) a branch of the jugular sac may enter the innominate 
vein a little anterior to the subclavian, but it is not clear that an actual 
opening exists and none can be found on the opposite side (p. 103). 
Finally, referring to a 21mm. rabbit of 17 days, he states that 
the jugular lymph sae on the left side, except for an extensive rupture 
does not connect with the vein. On the right, a pore is found leading 
from the sac to the internal jugular vein near its union with the external, 
but this also may be artificial. Thus in all the series of rabbits no bilateral 
communication of the lymphatics and veins, in the position of the adult 
openings, could be found. The pores, sometimes detected in various 
positions, are not adequate to empty the large sacs, and may indeed be 
artifacts. Communication with the veins in these must be by osmosis, 
therefore, and the permanent outlets of the lymphatic system must 
develop later (p. 109). 
The above quotations include all of the data given by Lewis 
which bear in any way upon the actual development of the jugu- 
lar lymph sacs. On examining these data it can be seen that his 
general statement, given in the Summary (p. 110), that the 
lymphatic system of rabbits (jugular lymph sac) begins along the 
internal jugular vein as a detached sac formed by the coalescence 
of several venous outgrowths, covers the general ground of lymph 
sac formation, but that his conclusions, while perfectly correct 
in their bearing on veno-lymphatic development, are based on 
insufficient observations. We therefore feel justified in making 
the statement at the beginning of our paper that our object in 
presenting so detailed an account is to place beyond the range of 
inference all doubt that has hitherto existed regarding the venous 
origin of the jugular lymph saes. Although Lewis has been justi- 
fied in drawing this inference, had he examined a large number 
of embryos of each stage, ranging between 6 and 14 mm. in length, 
he would have, unquestionably, been able to establish a definite 
venous origin for each of the segments of the lymphatic chain in 
the 10 mm. rabbit, without expressing any doubts whatever. 
Considering the fact that we now know the jugular lymph sac 
to be derived from the veins, the question arises as to the develop- 
