On the breeding of Eels. 109 
affecting the ear with sounds, and the eye by a modified reflee- 
tion of light. Where we perceive none of these usnal concomi- 
tants of matter, we are prone to infer its absence. Hence igno- 
rant people have no idea of air, except in the state of wind; and 
when even in a quiescent state designate it by this word. Bat 
that the principles, the existence of which has been demon- 
strated, should not be thus perceived, 1s far from being a reason 
for doubting their existence. <A very slight attention to their 
qualities will make it evident, that they could not produce atiy 
of the effects, by which the existence of matter in its ordinary 
form is recognised. The self-repellent property renders it im- 
possible that they should resist penetration; their deficiency of 
weight renders their movements nugatory. When in combina- 
tion, they are not perceived, but the /odies with which they com- 
bine; and it is only by the changes they produce in such bodies, _ 
or their effects upon our nerves, that they can be detected. 
XXIV. On the Breeding of Ecls. By Anruony Caktisiz, Esq. 
To Dr, Tilloch. 
Dear Sin,—Some years ago I suggested to several naturalists 
the probability that the common river eél effected its procreation 
exclusively in the sea; and as my professional engagements now 
supersede such pursuits, I submit my reasons for entertaining 
that opinion to persons who may have opportunities of ascer- 
taining the necessary proofs. It is notorious that the common 
eel is never taken in fresh water with either the male or female 
organs distinctly pronounced, It is also known that those fishes 
descend rivers toward the sea; and at those seasons they are 
caught abundantly in wears and by other contrivances: but those 
grown eels never return again up the rivers or streams, and there- 
fore either finally perish in the ocean or remain permanently for 
some special occasion. At particular periods small eels ascend 
rivers in vast shoals, and toward the mouths of rivers they are 
found of smaller dimensions, aud gradually attain growth as they 
advance up the streams; for example, the small grigs caught so 
copiously in wicker baskets, and in Chinese dipnets, or by bob- 
bing with threaded worms in the river Thames, are never found 
of the same small sizes toward Oxford, as they appear within the 
tiding range of the river. About three years since, when dis- 
secting a conger eel, | discovered a matured female roe, the ova 
being ripe for detachment from the parent membranes; and on 
comparing this animal with the common eel, [ could not discern 
any distinctive difference, either external or internal, beyond those 
trivjal deviations which ovcur to the species of many other erea- 
1 tures. 
