678 PROFESSOR T. WHARTON JONES ON THE CAUDAL HEART OE THE EEL. 
When the circulation in the tail is active and the blood flows with corresponding force 
in the great caudal venous trunk and its tributary vein, the blood-stream does not yield 
so readily, as above described, to displacement by the lymph-stream from the heart, but 
the propulsion of the drops of red blood presents a remittent rather than an intermittent 
character. 
Influence of the force with which the lymph-stream is propelled from the caudal heart in 
accelerating and promoting the flow of Mood in the caudal vein. 
The force with which the lymph is propelled by the heart into the caudal vein may 
be judged of comparatively by contrasting the force of the stream, as indicated by 
rapidity of flow, in the tributaries of the vein, with that of the stream in the vein itself 
whilst the lymph is being propelled into it. Within the vein, the force of the lymph- 
stream is evidenced by the fact above mentioned, that at the moment of the propulsion 
of the lymph into the vein by the contraction of the heart, the onward course of the 
blood in the tributary vein is arrested and the column of blood in the caudal trunk 
displaced to one side ; and also by the manner in which the drops of red blood or agglo- 
merations of red corpuscles, which enter the caudal trunk from the tributary vein during 
the diastole, are seen driven on in the lymph-stream at each systole of the heart. 
Through the medium of the stream of lymph propelled into the great caudal vein at 
each stroke of the heart, an impetus is communicated to the column of blood in that 
vessel, which we can observe has the effect of accelerating and promoting its onward flow 
to the blood-heart of the animal. 
We thus see that though the caudal heart of the eel is a lymphatic heart, its function 
being to receive lymph on the one hand and to propel it into the great vein of the tail 
on the other, it at the same time performs the secondary function of accelerating and 
promoting the flow of the blood in that vessel in its course back to the blood-heart. 
Teleologically speaking the great length of the tail of the eel seems to render a reason 
for such a provision. 
In respect to the secondary function of the caudal heart of the eel here mentioned, 
an analogy may thus be traced between it and the rhythmically contractile veins of the 
much elongated wing of the bat. 
How does the lymph enter the caudal heart ? 
This question does not properly come within the scope of the present paper. It may, 
however, be remarked that I have observed under the microscope no defined lymphatic 
vessels opening into the heart, and only an indistinct appearance of afferent streams of 
lymph. 
If there had been any lymphatic canals opening into the heart, such as those the late 
Professor J ohaottes Muller (in his paper entitled “ Beobachtungen zur Analyse der 
Lymphe des Blutes und des Chylus ” in Poggendorff’s Annalen der Physik und Chemie 
for 1832, page 519) states that he injected through a slit made into the organ, and if a 
