DEVELOPMENT OF LYMPHATICS IN ANURA 91 
a lucid idea of the morphogenesis of the anterior lymph heart is 
to examine a consecutive series of reconstructions representing 
different genetic stages. Such a series is pictured in figures 31 
to 35, inclusive, attention to which has already been directed in 
the preceding section on the development of the jugular lymph 
duct. 
The reconstruction in figure 31, reproducing the conditions in 
a 4-mm. embryo, shows the vague beginnings of the anterior 
lymph heart as an incipient vascular plexus between the second 
and the fourth intersegmental vessels and in connection with the 
proximal portion of the third. It is so inconspicuous and ill- 
defined that the observer would overlook it but for the striking 
changes that occur in the same locality soon after. 
In 5-mm. embryos, the above venous, or better, venolymphatic 
plexus, the anlage of the anterior lymph heart, has become more 
sharply outlined. In comparison with the preceding stage, the 
plexus not only has joined the second and fourth intersegmental 
vessels by longitudinal anastomosis, but also has increased the 
number of its connections with the pronephric sinus from one, 
the original mouth of the third intersegmental, to several. 
By the distention of the interjoined channels of the lymph- 
heart plexus, these coalesce, resulting in a single cavity. In 
figure 32 the loop-hole in the anterior part of the anlage is still 
indicative of its previous plexiform state. Viewed from the side, 
as pictured the contour of the anlage already suggests its future 
globular form. In reality, however, its shape at this time is 
lenticular, for its lateromedial diameter is not much greater than 
the third intersegmental vessel from which it sprang, and accord- 
ingly in transverse section through its center (fig. 17, cor. lym. 
ant. sin.) it would appear as a spindle-shaped expansion of this 
vessel. The connection of the heart with the pronephric venous 
sinus and with the surrounding intersegmental network, which, 
as already shown, is involved in the formation of lymphatic ducts, 
vary little in position and in number, as a comparison of several 
specimens of the same age has shown. At the lower margin of 
the lymph-heart anlage (fig. 32) the delta-like confluence with 
the pronephric sinusoids is to be regarded as a complication of the 
