In the land Prosobranchiata (Cyclostomatidae, Cyclophoridae, Aciculidae, Helicinidae) which, having exchanged a marine for an aerial life, breathe air instead of water, the branchia has completely disappeared, and breathing is conducted, as in the Pulmonata, by a lung-cavity. In certain genera of land operculates, _e.g._ _Pupina_, _Cataulus_, _Pterocyclus_, a slight fissure or tube in the last whorl (see Fig. 180, p. 266) serves to introduce air into the shell, which is perhaps otherwise closed to air by the operculum. In _Aulopoma_, which has no tube, the operculum admits free circulation of air. In certain other Cyclostomatidae the apex is truncated, and air can enter there. De Folin closed with wax the aperture of _Cycl. elegans_, and found that on placing it in a pneumatic machine, the shell gave off air through its whole surface. On the other hand, _Cylindrella_ and _Stenogyra decollata_, on being submitted to the same test, showed that the truncated part alone was permeable by air. Fischer and Bouvier have made some interesting observations on the breathing of a species of _Ampullaria_ (_insularum_ Orb.). The species has, in common with all _Ampullaria_, two siphons, but while the right siphon is but slightly developed, the left is very long, almost twice as long as the shell (see Fig. 65). The animal, when under the water, lengthens its siphon, brings the orifice to the surface, and by alternately raising and depressing its head produces in the pulmonary sac movements of ex- and inspiration; these are repeated about ten or fifteen times at regular intervals of from six to eight seconds, a method of respiration strongly resembling that of the Cetacea. At the same time, branchial respiration takes place. If powdered carmine is added to water, the particles are seen to enter the branchial cavity by the siphon and pass out by the short right siphon. Sometimes the animal remains under water for hours without rising to the surface to inspire air. In _Valvata_ (Fig. 66) the branchia is very large, and projects like a leaf or fan above the shell on the left side; on the corresponding position on the right side is a long filiform appendage, which some have regarded as representing the other branchia. [Illustration: FIG. 65.--_Ampullaria insularum_ Orb.: =A=, breathing water; =B=, breathing air; =Si=, siphon; =T=, upper; _t_, lower tentacles; =X=, pallial expansion, performing the part of excurrent siphon. (After Fischer and Bouvier, x ⅓.)]