32 HIRUDO. 
out the system, by means which merit the attention of those investigat- 
ing the comparative anatomy of animals. The natural and favourite 
prey, however, seems to be the Helix peregra, within which, as an insi- 
dious and implacable enemy, it wages perpetual and destructive war. 
None of the leeches are deterred by disparity of size, or of strength, 
from the attack. The smaller, as well as the larger, assail their objects, 
regardless of the external safeguard provided by nature. The leech be- 
comes quickly sensible of the introduction of its prey into the same 
vessel. Then relaxing from its wonted sluggishness, it begins to mani- 
fest symptoms of activity. Meantime the victim shews no apprehension 
at the advance of its deadly enemy, nor does it make any attempt to 
escape. One or two leeches now seat themselves on the shell, and as the 
tenant protrudes freely, they stretch their heads towards the opening, en- 
deavouring to insinuate them within, whereby a lethal wound may be in- 
flicted on some remote organ. The prey then struggles violently to free 
itself, but in vain. The assailant, adhering firmly by the sucker, cannot 
be dislodged ; and these very exertions for liberation from its enemy, which 
might be most effectual in shaking off another invader, tend to expose 
the body still more to invasion. The creature seems to become incapable 
of retreating within the shelter of its impenetrable dwelling, and of closing 
up the entrance for protection. While ascending the sides of the vessel 
to free itself of such an oppressive incumbrance, its life is gradually 
wasting, the faculty of adhesion fails, and it tumbles to the bottom, over- 
come by its merciless foe. 
Whether the victim perishes first by exhaustion of the fluids or con- 
sumption of its flesh, is uncertain ; but the darkening of the intestinal 
pouches of the assailant shews that it has fed copiously on the prey. 
These pouches are rendered exceedingly conspicuous, displaying their 
regular distribution, and the peculiar conformation of the lowest pair. 
Disparity of size is no protection to the Helix, for the largest of the 
prey seems unable to contend with the smallest of the enemy. On one 
occasion two leeches of inconsiderable size advanced to the attack, each en- 
deavouring to insinuate its head under the victim’s shell. The first retired 
without having produced any sensible effect ; the second persisted perti- 
