50 . HIRUDO. 
Though active m the finer season, these animals generally shun the 
light ; its presence seems to create uneasy sensations. But it must appear 
somewhat remarkable, that in the Hirudo muricata or Skate Leech, no 
organs of vision have been:as yet discovered. 
Leeches are extremely dependent on the temperature of the atmo- 
sphere. What is genial to most other animals is refrigerating to them, and 
at a very moderate degree torpor succeeds activity. All are extremely 
voracious whenever opportunity offers, greedily devouring fish, flesh, and 
other animal substances. Nor are the succulent parts of vegetables al- 
ways rejected. Their voracity is such that they obviously perish of 
mere repletion. The muricata, medicinalis, and sanguisuga absorb blood 
in great quantities, but it does not seem to be the aliment of some 
others. We have seen how bold and insidious an enemy one may be, from 
which there is no escape, and which nothing less than the life of its 
victim can satisfy. 
A few breed readily in confinement, but rarely those the most valuable 
to mankind. Of others it seems almost impracticable to obtain the pro- 
geny. The propagation of a few, however, discloses some interesting facts 
in physiology. 
It is a cruel and a common error, to believe that the Medicinal 
Leech can sustain life on water alone, and that withont renewal. Un- 
equivocal symptoms demonstrate that emaciation is inseparable from 
abstinence, and that nothing is so grateful as general warmth and the 
renovated element. 
It does not appear that the history of the leech has advanced in pro- 
portion to the number of the literati who have rendered it the subject 
of discussion. 
