VI 



BREATHING ORGANS IN PULMONATA 



l6l 



hibernation, a snail 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 procure it, and that they perish, 

 if prevented from doing so, by asphyxiation. If, we are told,i 

 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 



Fig. 71. 



Limax maximus L. : PC, pulmonary 

 orifice, x |. 



Fig. 70. — Janella hirudo 

 Fisch., N. Caledonia: 

 G, generative orifice ; 

 P, pulmonary orifice ; 

 T, T, tentacles. (After 

 Fischer.) 



foot, it will sink heavily to the bottom, emitting a stream of air 

 from its pulmonary orifice. On recovering from the shock, it 

 will anxiously endeavour to regain the surface, but will have 

 some difficulty in doing so, owing to its now much greater 

 specific gravity. When 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 life. Moquin-Tandon, on the other hand, is 

 1 Zoologist, xii. p. 4248. 



VOL. Ill M 



