676 PEOEESSOE T. WHAETON JONES ON THE CAUDAL HEAET OE THE EEL. 
Being laid on the slide with the tail in proper position, the animal was fixed by tying 
a string loosely round the slide and its body where enveloped in the rag. 
The part of the tail to be examined was covered with water and a thin plate of glass. 
Matters being thus arranged and the microscope adjusted, rapid pulsations are imme- 
diately detected, on directing the eye to the region of the extreme end of the vertebral 
column — abdominal side*. 
No very well-defined heart-like organ is observable at first sight, but the pulsations 
seem as if in the tissue of the part generally. The skin and substance of the tail sur- 
rounding the heart are drawn somewhat together at each systole, and fall back into their 
previous state at each diastole. From this it may be inferred that the heart does not 
lie free in a special cavity, nor even in loose cellular tissue, but that it is imbedded in 
the substance of the tail. 
Dissection of the tail of a large eel shows that the heart is connected with the adjacent 
bonesf. 
The great vein of the tail $ is formed by the junction of two trunks, a larger and a 
smaller §. The larger trunk receives the venous radicles returning the blood from the 
terminal and abdominal parts of the caudal fin. The smaller trunk receives the venous 
radicles returning the blood from the dorsal part. 
It is into this smaller trunk, near its junction with the larger, that the caudal heart- 
opens. 
The great artery of the tail || runs close alongside the vein, and is smaller than it, 
and somewhat tortuous. It gives off branches to the abdominal and dorsal parts of the 
caudal fin, whilst the continuation of it subdivides into the small ramifications distributed 
to the terminal part. 
This continuation of the artery and the larger trunk of the great caudal vein diverge 
from each other in their course towards the end of the tail, and then, after having 
become small by the giving off of branches, approach curvingly and cross each other at 
the place where the spine ends and the terminal part of the caudal fin commences. 
The elongated space bounded by the artery and vein thus diverging from* 1 and again 
approaching each other, is that in which the lymphatic heart is situated^] - . 
Description and explanation of the phenomena attending the propulsion of the lymph from 
the caudal heart into the caudal vein. 
At the opening of the caudal heart into the vein there is a valve which prevents 
regurgitation of the lymph back from the vein into the heart ; but, owing to the thick- 
* Plate XXXY. figs. 1 & 2, E. 
t This point in the anatomy of the candal heart is described in detail in Part III. of my paper entitled, 
“ Microscopical characters of the rhythmically contractile muscular coat of the veins of the Bat’s wing, of the 
lymphatic hearts of the Erog, and of the caudal heart of the Eel.” 
t Kate XXXY. figs. 1 & 2, B. § Plate XXXY. figs. 1 & 2, C, D. 
|| Plate XXXY. fig. 1, A. f Plate XXXY. fig. 1, E. 
