Page:British Reptiles, Amphibians, and Fresh-water Fishes.djvu/76

BRITISH FRESH-WATER FISHES silvery-white in colour, with bluish or greenish on the back. It attains a maximum length of about i6 inches, and is a common inhabitant of many of our larger rivers, especially the Severn. It has only one nasal opening, but makes up for this by having seven small gill-slits on either side of the body at the back of the eye. There are no fins along the front two-thirds of the body-length, and even then only a small, succeeded by a larger one, is present on the back, and the pointed tail is more or less finned above and below. Lampreys possess a sucking disc, and with this they attach themselves to their prey. It seems agreed that they belong to a very low type of animal life, but in spite of this their metamorphosis is most interesting, and we have a good deal to learn respecting them. Some individuals appear to spend their whole time in fresh water, others proceed to the sea, ascending rivers, like the Salmon, for spawning. This latter event happens in Autumn or Winter, and the Lamperns, as they are also called, gradually make their way nearer the source of rivers until they have travelled so far that only small tributaries of the main artery are occupied. They delight in a gravelly bed, and are of social habits, for little companies of thirty or forty assemble together in Spring and early Summer. Although so low in the scale of life, Lampreys construct a "nest," and it is interesting to note that several pairs will share the one abode. Their ideas on co-operation are, to say the least, put to a very practical test. A word should be written as to the "nest" as it merely consists 60