DEVELOPMENT OF LYMPHATICS IN ANURA 93 
In 7-mm. embryos, the connections between the lymph heart 
and the cireumjacent venolymphatic plexus begin to break away. 
An early stage in this process is shown in figure 33. The anterior 
connection is still broad; on the dorsal surface of the heart one 
has already severed relations and another is very much con- 
stricted; the one on the posterior surface, too, shows signs of 
contraction when compared with its homologue in figure 32. On 
the ventral aspect of the heart one channel of confluence is just 
being pinched off, but the more anterior connections are fusing 
into one and so constitute the anlage of the anterior vertebral 
vein and the lymphaticovenous tap. During these progressive 
events, the heart becomes more spheroidal as the area between 
the myotomes and the epidermis widens, associated with the 
rounding out of the back and sides of the embryo (fig. 18). 
In 8-mm. embryos, mere vestiges, in the form of small pro- 
jections, remain of the former union between the lymph heart and 
the neighboring lymph vessels, as delineated in the reconstruction 
in figure 35, but in every case their coincidence with the points 
of union of earlier stages can be made out readily. At this period, 
then, there seems to be no open passage whatsoever between the 
cavity of the lymph heart and the remainder of the lymphatic 
conduit system. It is a blind globular chamber attached to the 
anlage of the vertebral vein at its anterior and ventromedial 
surface and is confluent with it. 
During the period between 8- and 10-mm. stages the secondary 
or permanent communication is established between the lymph 
heart and the afferent lymph duct. A comparison of figures 34 
and 35 and the photomicrographs, figures 19 to 28, shows plainly 
how this is accomplished. By uniform growth and dilatation of 
the lymph heart as well as of the cireumjacent lymph vessels, 
the common segment of the jugular and lateral ducts (lym. com. 
jug. et. lat.) and the dorsal aspect of the heart are gradually 
brought together, this approximation continuing until the duct 
comes to lie in a shallow groove-like indentation or depression of 
the heart wall. Along this line of contact the first afferent 
ostium appears. In later stages, as more tributaries of the afore- 
said lymph channels are formed, some of them, situated nearest 
the heart, cross over its surface and come to lie against it, and 
