BREATHING ORGANS IN PULMONATA 



i6i 



breathes at all. In any case, the amount of air required to 

 sustain life must be small. 



With regard to the respiration of fresh-water Pulmonata there 

 appears to be some difference of opinion. It is held, on the one 

 hand, that the Limnaeidae only respire air, making periodic visits 

 to the surface to procm-e it, and that they perish, if prevented 

 from doing so, by asphyxiation. If, we are told,^ as a Limnaea 

 is floating on the surface of the water in a glass jar, a morsel of 

 common salt be dropped upon its outstretched foot, it will sink 



Pig. 70. Janella hirudo Fig. 71. — Limax mnximus'L.: PO, pulmonary 



Fiscli., N. Caledonia : orifice. x §. 



G, generative orifice ; P, 

 pulmonary orifice ; T, T, 

 tentacles. (After Fis- 

 cher. ) 



heavily to the liottom, emitting a stream of air from its pulmon- 

 ary orifice. On recovering from the shock, it will anxiously 

 endeavom' to regain the surface, but will have some difficulty 

 in doing so, owing to its now much greater specific gravity. 

 AVhen it succeeds, it creeps almost out of the water, and exposes 

 its respiratory orifice freely to the air. If the experiment is 

 repeated several times on the same individual, it becomes so much 

 weakened that it has to be taken out of the water to save its 



^ Zoolorjist, xii. p. 4248. 



VOL. Ill 



M 



