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Show 1870.J AND ECONOMY OF THE LAMPREYS. 849 the bristle a a is passed from the peritoneal sac, through the tubular genital outlet which perforates lengthwise the centre of the papilla; the bristle b b is passed along the inside of the intestine, and out at the anus. In the female, fig. 5, some ova are seen free in the abdomen, and others passing and passed through the canal ot the vulva. Fig. 6, spermatic filaments, magnified about 700 diameters. Fig. 7, marginal papillse of the dorsal fin, magnified about 75 diameters. Fig. 8, a bit of fin-ray, its cartilage-cells and sheath-fibres, magnified about 600 diameters. Fig. 9, brain-worm, enlarged about 60 diameters. All the figures were taken from Planer's Lamprey. Abundance of Ova.-The females of Planer's Lamprey are much distended with eggs in the spring. In a specimen of Petromyzon fluviatilis caught on the 20th December, 1868, eighteen inches long and six and a half ounces weight, I counted no less than 51,220 eggs, none of which were then detached from the ovary into the peritoneal cavity. Their average diameter was -^ of an inch ; and 394 of them, after having been drained of extraneous moisture, weighed one grain. PETROMYZON PLANERI. I have seen this species in abundance at Dundrum in the north of Ireland; and it is remarkably plentiful in the river Stour at Canterbury. During the spawning-season, which occurs here from the end of March until June, this Lamprey is so common in tbe shallow streams, and so intent on the procreative business, as to be taken in numbers by hand, much to the amusement of the idle boys, who indulge then in this simple and primitive sort of piscatorial sport. After June or July, these Lampreys entirely disappear, so that not a single specimen can be found, though the larval Ammocete is then, as before, to be caught. During the height of the spawning-season, Planer's Lamprey takes so little food that none is found in the alimentary canal, which is then contracted to a mere thread, while the Ammocete feeds freely and has its intestine distended accordingly. ENTOZOA. It is remarkable that a fish with its brain-case occupied by a mass of living worms equal to that of the cerebral substance should appear in perfect health and activity, exercising its generative functions with the greatest vigour ; yet such is the case with Planer's Lamprey. In the course of last spring my son was examining the brain of this fish, and found it infested by great numbers of what seemed to belong to the tribe of parasitic " platyelminthes." Of a single fish the entire brain was not larger than the aggregate bulk of the whole of these worms. On pursuing the inquiry, it was found that every Planer's Lamprey taken for us that season from the Stour river at Canterbury was thus infested; not a single specimen examined was exempt from these brain-worms. Their future career and |