1870. | AND ECONOMY OF THE LAMPREYS. 849 
the bristle @ a is passed from the peritoneal sac, through the 
tubular genital outlet which perforates lengthwise the centre of the 
papilla; the bristle 6 6 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 
ef the vulva. Fig. 6, spermatic filaments, magnified about 700 
diameters. Fig. 7, marginal papilla 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. Ina 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 
eges, none of which were then detached from the ovary into the 
peritoneal cavity. Their average diameter was qs 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 Can- 
terbury. During the spawning-season, which occurs here from the 
end of March until June, this Lamprey is so common in the 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 accord- 
ingly. 
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 
helong 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 Poin the Stour 
river at Canterbury was thus infested; not a single specimen exa- 
mined was exempt from these brain-worms. ‘Their future career and 
