SPECIAL ANATOMY. 201 
between it and the extremity of the pedal disc. The 
anal aperture opens at the posterior margin of the latter 
orifice. The generative apparatus has two distinct ex- 
ternal apertures, distant from each other. The male 
genital orifice is placed just beneath the mouth, between 
it and the blind sac, inclining to the right. The female 
orifice is situated upon the inferior part of the left side 
of the mantle, midway between the head and tail. 
As usual, the body has two cavities, of which the pul- 
monary occupies a position at the right posterior part, 
beneath the mantle, and extending backwards on the 
right to the tail. 
Chapter ii. — general remarks on the terrestrial 
testaceous gasteropoda. 
A testaceous gasteropod resembles a slug with the 
greater portion of the viscera scpieezed out upon the 
back, and arranged in a turbinate manner. The turbin- 
ate mass is always an exact mould of the testaceous cover- 
ing of the animal ; its length in the spiral direction holds 
no proportion with that of the foot, or that part of the 
body which the animal protrudes from the shell, and dif- 
fers very much, not only in different genera, but also in 
different species of the same genus. With an increase 
in length a proportionate decrease in breadth is observa- 
ble, and vice versa. In Pirpa it reaches its maximum 
length and narrowness ; in Succinea it has the mini- 
mum length, and the greatest proportionate breadth. 
vol. i. 52 
