682 PROFESSOR T. WHARTON JONES ON THE CAUDAL HEART OF THE EEL. 
attenderem ad magnara arteriam in cauda jacentem, ibi protrusio sanguinis, a corde facta, 
multo erat vehementior ” might be admitted as having reference to the phenomenon of 
the transmission of the drops of red blood or agglomerations of red corpuscles in rapid 
succession along the caudal vein, opinions may perhaps differ, but certainly all will 
agree with me that no one could have been led by the words to suppose that Leeuwen- 
hoek was speaking of a heart in the tail of the eel. 
Had it been the caudal heart to which Leeuwenhoek refers, however, and not merely 
the branchial heart of the fish, he would, no doubt, have commented on the peculiarity 
of its position in the tail, and expressed as much admiration, at least, as he does at the 
general phenomena of the circulation in the fins of the eel, when he says, unwilling 
to reserve to himself so beautiful a sight, he invited several “ Viri gravissimi ” to come 
to see it — amongst others the celebrated Christian Huyghens. These gentlemen, he 
tells us, “ often exclaimed that they could not have believed anything more curious 
could have met their eye or been better demonstrated.” 
Explanation of the Plate. 
PLATE XXXV. 
Fig. 1. The caudal artery and its ramifications, the caudal vein and its two tributary 
trunks with their radicles, and the caudal heart, as seen in a small eel 
under the microscope. 
No capillaries are represented. 
A. The caudal artery, the ultimate ramifications of which are seen distri- 
buted in straight lines corresponding with the direction of the rays of the 
caudal fin. 
B. The great caudal vein formed by the junction of the two tributary trunks 
C and D. The radicles of these trunks are seen parallel with the straight 
ultimate arterial ramifications. 
E. The caudal heart communicating, by an opening provided with a valve, 
with the smaller tributary caudal venous trunk D, near where it joins the 
larger tributary caudal venous trunk C to form the great caudal vein B. 
The smaller tributary venous trunk D, from the place where the caudal 
heart opens into it to its junction with the larger tributary trunk C, to form 
the great caudal vein B, is seen filled with the lymph-stream just propelled 
into it from the heart, whilst in the great caudal vein the lymph, still under 
the influence of the heart’s force, has so far displaced the blood as to flow for 
some distance in a colourless stream on one side of the vessel. 
Fig. 2. A diagrammatic view of the caudal heart, and the lymph-stream from it, with 
the drops of blood or agglomerations of red corpuscles which issue, one from 
