342 
WILLIAM V. ALLEN. 
mimicates above with the caudal heart, but about the orifice- 
tliere is a slight massing ot‘ the mesenchyme (Fig. lb, veil. (]) ) 
possibly indicative of the beginning of valves, and the 
anterior ending of this cavity under the embryonic lateral 
process of the median ventral bar resembles the ending of the 
first cavity of the 25 mm. series. The third and fourth 
cavities (/. v. r, ( 3 )^ ( 4 )) have also united, but the fifth 
(/. V. V. ( 5 )) is still isolated. While the fourth cavity has gained 
connection with the left caudal heart there is at present no 
trace of valves at the orifice. Both the second and the fourth 
cavities have joined two isolated mesenchymal cavities 
(L. L. tl. C.) belonging to the left embryonic lateral veno- 
lymphatic sinus, and the third mesenchymal cavity has 
gained direct connection with the left lateral sinus, doubtless 
through a union of certain of the lateral sinus mesenchymal 
spaces. It might be said for both embryonic ventral veno- 
lymphatic trunks of the 27 mm. series that they consist of at 
least five,' more or less, connected cavities situated directly 
below the caudal heart ; that they have obtained connection 
with both the lateral sinuses and the caudal heai-ts, and these 
vessels have now obtained a len gtii equal to that of the 
caudal heart. 
Keconstruction 8 of the 60 mm. series shows the left ventral 
veno-lymphatic trunk (L. V. V.) to have assumed practically 
adult conditions in the region of the caudal heai-t, with the 
exception that there will be found in a few places the remains 
of former mesenchymal cavity partitions that have not com- 
pletely disintegrated. The orifices of the anterior and 
posterior communications lyetween the yentral trunk and the 
left caudal heart are guarded by valves, well developed in the 
former and in the process of formation in the latter. 
Xumerous connections {L. L. S. Con.) have been received from 
the left lateral sinus, and immediately jn front of the caudal 
hearts the three terminal branches of the posterior portion of 
the longitudinal TuTBiiial lymphatic trunk will be found ta- 
culminate. ' . . -■ ‘ 
