S4 OTTO F. KAMPMEIER 
ganglia® and a segment of the neural tube, were introduced in 
the reconstructions for the purpose of orientation. 
I (20) deseribed the series of intersegmental vessels that 
appear in the development of the venous system as dorsal tribu- 
taries of the pre- and postcardinal trunks and found them situated 
at the intersegments of successive myotomes. ‘The first two 
reconstructions (figs. 31 to 32), besides illustrating the beginning 
of the anterior lymph heart as a circumscribed plexus of the prox- 
imal portion of the third intersegmental, shows the development 
of a more open-meshed network of vessels formed by anastomoses 
between the first, second, and third intersegmentals. The 
jugular lymph duct is derived from the latter plexus. Passing 
from the 6- to the 7-mm. stage, the genetic changes consist in 
the separation of this intersegmental plexus (which in view of its 
former and its future functions may temporarily be called a 
venolymphatic) from the precardinal vein and the pronephric 
venous sinus. The channels of connection contract in caliber, 
like any other small redundant vessel, and finally are cut off 
entirely. This is indicated in the reconstruction in figure 33, 
where the points marked by a star still show minute and slender 
connections, the last traces of the originally freely confluent 
condition of the intersegmental veins and their parent trunk. 
Farther forward in the figure are two other vestiges in the form 
of venous spurs extending towards the lymphatic duct. As the 
veno-lymphatie plexus (potentially lymphatic) is severed from 
the veins, its channels distend, evidently due to the accumulation 
of the lymph within their lumen. 
While the foregoing is taking place, a notable event, the tran- 
sient isolation of the lymph heart anlage from the surrounding 
lymphatic plexus, occurs, a process which will be considered more 
fully in the following section. Such a phase is illustrated in the 
reconstruction in figure 34. The secondary junction between 
heart and afferent lymphatic is brought about a little later. The 
2 The first pair of spinal ganglia are evanescent structures in the anourous 
Amphibia, being present in toad embryos (B. vulgaris) only during the 6-mm. 
stage and vanishing completely very soon after. The second pair become the 
first of the adult. 
