THE GASTROPODA 183 
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of the oviduct and penis may be approximated, a condition found 
in the majority of the Stylommatophora (Fig. 104). 
The Pulmonates never have a free larval form; if a veliger is 
developed it is always contained in the egg membranes. The 
majority of Stylommatophora do not pass through a veliger stage, 
and in other forms the velum is almost always ill developed (Fig. 
A series of Stylommatophorous Pulmonata, showing the reduction of the shell. A, Helix 
pomatia ; B, Daudebardia brevipes ; C, Testacella, haliotidea; D, Arion ater. a, external shell in 
‘A, B, C; shell-sac (closed) in D; b, orifice of the pallial or pulmonary cavity. - (From Lankester, 
after Ferussac, Pfeitfer, and Reeve.) 
119, A, ve). The Pulmonates are for the most part aerial, but 
some live in fresh water, and others, but they are exceptional cases, 
are marine. The Pulmonates are distributed over the whole world, 
and include some seven thousand species, of which more than half 
belong to the genus Helix. Most of them enter into a resting stage 
during some part of the year; in the summer in hot climates, in 
the winter in cold climates. In our country the hibernation lasts 
for rather more than a third of the year. 
