108 OTTO F. KAMPMEIER 
Since blood cells have free access to the cavity of the lymph 
heart before the appearance of the valve at the lymphatico- 
venous junction, in stages up to and including 10-mm. embryos, 
they are abundant in it (figs. 18 to 22 and 25). In 12-mm. 
embryos and later (figs. 23 and 26), they are rarely present, and 
we may conclude from this and the fact that the valves are now 
functionally complete and efficient that the pulsations of the 
lymph heart commence at this time, for the first few contractions 
would certainly cause the evacuation of all haemal elements. 
On account of the abundance of pigment in the integument of 
Bufo embryos, it was impossible to determine accurately by direct 
observation on the living specimen at which time the pulsations 
of the anterior lymph heart commenced, but, according to Hoyer 
(05), they first become evident as irregular quiverings in the 
more transparent frog embryos (R. temporaria) when they are 
12 to 18 mm. long. Later the pulsations of the lymphatic heart 
become more rhythmic, but the beats coincide neither with those of 
the haemal heart nor with those of its companion on the opposite 
side. In the mature animal it throbs as often as sixty to seventy 
times every minute, and since its capacity is about 0.5 cu. mm. 
(Radwanska, ’06), the quantity of lymph pumped into the 
anterior vertebral vein during this period is 30 cu. mm., and in 
one hour reaches the relatively considerable amount of 180 cu. 
mm. During systole of the lymph heart, the efferent valve, 
projecting into the vein, opens for the discharge of the lymph, 
but closes and prevents the backflow of blood into the heart 
chamber during diastole. Similarly, the afferent gateways per- 
mit the entrance of the lymphatic current from the cireumjacent 
lymph sinuses, yet avert its reflux during systole. 
