rivers in the summer; and some idea of the numbers of these young eels, each about three inches long, may be gathered from the record of Dr. William Roots, who lived at Kingston in 1832. He calculated that from sixteen to eighteen hundred passed a given point in the space of one minute of time. These baby-eels travel only by day and rest by night. In large and deep rivers, where they probably find the current strong, they form themselves into a closely compacted company, "a narrow but long-extended column," as it has been described; but in less formidable streams they abandon this arrangement and travel, each one more or less at his own sweet will, near the bank. The perseverance of these little creatures in overcoming the obstructions they may encounter is quite extraordinary. The large flood-gates, sometimes twenty feet high, that are to be met with on the Thames would be sufficient, one would imagine, to bar the progress of a fish the size of a darning-needle. But young eels have a wholesome idea that nothing can stop them, consequently nothing does. As one writer says, speaking of the way in which they ascend flood-gates and such like barriers, "Those which die stick to the posts; others which get a little higher meet with the same fate, until at last a sufficient layer of them is formed to enable the rest to overcome the difficulty of the passage." The mortality resulting from such "forlorn hopes" greatly helps to account for the difference of number between the upward migration of young eels and the return of comparatively few down-stream in the autumn. In some places these baby-eels are much sought after, and are formed into cakes which are eaten fried. On one occasion at Exeter two cart-loads of these little fish, not larger than darning-needles, were sold, each cart-load weighing four hundredweight. They were sold for four-pence per pound. The term elver, which, as we have said, is in some places indiscriminately used to denote all young eels, in reality only belongs to the "transparent" eels which are occasionally found among their more opaque brethren. These elvers are so transparent that most of the internal organs and the action of the heart and blood-vessels can easily be seen. Little is known of them. They are not supposed to form a distinct species, for they have been found with the characteristics of both sharp-nosed and broad-nosed eels. They have been met with in the rivers in January as well as in June, and, even when caught and confined in a tank, they in no way grow out of their peculiar transparency; so they have remained one of the many mysteries of the eel family till now. They are doubly interesting to study on account of this transparency. One of the greatest peculiarities possessed by eels is that they have a second heart situated in the extremity of their tails; of course, in the transparent elvers the action of this heart can be more easily noted than in the ordinary eels. In all, however, its action is plainly manifest, especially if the fish has been out of water any time or exhausted, a fact known to the street venders of live eels, who therefore are care-
