them is to obtain a portion of the eel's skin, from the belly, when the scales may there be observed in their natural position.

To omit notice of those common fishes, the Sticklebacks, would show how little the habits of these freaky creatures had been observed by us. Yarrell enumerates seven species as decidedly British.

Fig. 15.

RUFFLE

Scale of Grayling (Thymallus vulgaris).

Strange to say, many of these are purely marine in their habits, thus indicating a degree of specialisation, or adaptation to varying circumstances, on the part of the genus, which may have been the result of physical geological changes. Others, such as the Rough-tailed Stickleback (Gasterosteus aculeatus) live both in fresh and salt water, and so far connect the

extreme habits. This is by far the commonest of its kind, and is to be found in every river, stream, and

Fig. 16.

Scale of Barbel.

tarn, as well as all round the coasts, in Great Britain, from John o'Groat's to the Land's End.

Fig. 17.

The males are well known for their pugnacity, and for the beautiful colours of scarlet and green they put on in the spring, at the time when they make their aquatic nests. For, strange to say, this and one or two others are genuine nest builders! Towards the middle of April they may be observed (if kept in a fresh-water aquarium), collecting small pieces of stick and wet moss, so saturated that they cannot float. A pile of these is made, with a hole on the top. The sticklebacks then collect, with their mouths, fine sand, and trickle it all round the little cone. Woe be to any invader of this little nest, after it has been formed, and the female has deposited her ova therein ! Small as the three-spined stickleback is indeed, perhaps, the smallest of all our British species-it does not hesitate to attack much larger individuals, and will even tilt at the stick you point towards the little nest it is guarding! The ova hatch in

Scale of Eel, magnified.

ten days or a fortnight, the young remaining in the nest until the yolk-bag is absorbed. This is the signal for the male to leave them to themselves, for they are now supposed to be able to start in the world for themselves, and no longer to require paternal supervision. Not unfrequently, the conFig. 18.

Three-spined Stickleback and Nest.

stant care on the part of the parents in guarding the nest when the young are there, results in death. Indeed, it is a common occurrence for the parents to sicken and die through overmuch watching. These facts in the history of, perhaps, the commonest of our piscine tribes, render it a most interesting object for the aquarium. Among other allied species to be met with are the Smooth-tailed

Stickleback (G. leiurus), in which the males exhibit similar variations of colour, generally crimson and purple; and the Ten-spined Stickleback (G. pugnitius), which also lives alike in fresh water and salt, migrating up our rivers in shoals in the spring. All the sticklebacks are most voracious, as every boy who has angled for them is well aware.

Space does not allow us to do more than point out the evidence our fresh-water fishes, shells, and aquatic plants afford of the very recent separation of Great Britain from the main-land of Europe. And what they indicate is abundantly verified by the strata of the most recent deposits. We have no aquatic plants, or mollusca, or fresh-water fish, that are not common to continental rivers, lakes, and ponds. And our English stock must have extended over English latitudes before the formation of the German Ocean, for they could not have crossed the salt sea, and been imported in that way. Hence, although geologically speaking these familiar objects have been in existence, in England at least, only a comparatively short time, if we reckoned their occupation in numbers of years we should nevertheless be startled at the amount. Consider the great physical changes that have taken place since they extended hither the depression of the lowest levels on the eastern side of England to form the German Ocean, the submergence of the great plain to the west, to form the Irish Sea. Both these seas are shallow, and indicate recent formation. And the occurrence