or striding with rapid movements
across the gravel. Whence do they re-appear? Do they, too, take a
"summer sleep," like the reptiles, molluscs, and tank fishes, or may
they be, like the _Rotifera_, dried up and preserved for an indefinite
period, resuming their vital activity on the mere recurrence of
moisture?

Besides the medicinal leech, a species of which[1] is found in Ceylon,
nearly double the size of the European one, and with a prodigious
faculty of engorging blood, there is another pest in the low country,
which is a source of considerable annoyance, and often of loss, to the
husbandman. This is the cattle leech[2], which infests the stagnant
pools, chiefly in the alluvial lands around the base of the mountain
zone, to which the cattle resort by day, and the wild animals by night,
to quench their thirst and to bathe. Lurking amongst the rank vegetation
which fringes these deep pools, and hid by the broad leaves, or
concealed among the stems and roots covered by the water, there are
quantities of these pests in wait to attack the animals that approach
them. Their natural food consists of the juices of lumbrici and other
invertebrata; but they generally avail themselves of the opportunity
afforded by the dipping of the muzzles of the animals into the water to
fasten on their nostrils, and by degrees to make their way to the deeper
recesses of the nasal passages, and the mucous membranes of the throat
and gullet. As many as a dozen have been found attached to the
epiglottis and pharynx of a bullock, producing such irritation and
submucous effusion that death has eventually ensued; and so tenacious
are the leeches that even after death they retain their hold for some
hours.[3]

[Footnote 1: _Hirudo sanguisorba._ The paddifield leech of Ceylon, used
for surgical purposes, has the dorsal surface of blackish olive, with
several longitudinal striae, more or less defined; the crenated margin
yellow. The ventral surface is fulvous, bordered laterally with olive;
the extreme margin yellow. The eyes are ranged as in the common
medicinal leech of Europe; the four anterior ones rather larger than the
others. The teeth are 140 in each series, appearing as a single row; in
size diminishing gradually from one end, very close set, and about half
the width of a tooth apart. When of full size, these leeches are about
two inches long, but reaching to six inches when extended. Mr. Thwaites,
to whom I am indebted for these particu