70 LAND AND FRESH-WATER MOLLUSKS. 
Cuvier writes, that “the finest injections do 
not produce anything more agreeable to the eye 
of the anatomist than the white ramifications of 
the arteries in the black slug.” The arteries 
are opaque and milk-white, and strongly con- 
trast with the dark grounds upon which they 
trace their course; as, for example, the dark 
green of the intestines, or the blackish-brown 
of the liver. The heart is mcluded in a very 
thin bag’, or pericardium, in the cavity of which 
there is abundance of a watery fluid, as clear as 
crystal. 
Arion ater frequents damp and shady woods 
and thickets, gardens, and hedge-banks; during 
the day it is never seen abroad, except after rain, 
retirmg under stones and logs of timber, or 
burying itself in the earth; for the dry atmo- 
sphere would deprive the body of its moisture, 
so essential to the existence of the animal. 
It deposits its globular, semi-transparent eggs 
in May, among the roots of plants. This slug, 
as also some other of the larger species, is 
infested by a small yellowish-white mite, 
Philodromus limacum of Jenyns, who has given 
a very interesting account of the habits of the 
little animal. The parasites may be seen running 
in some numbers over the body of the slug. It 
is curious that the slimy surface of the slug’s 
back does not impede the progress of these . 
