RAMANAN : OX THE HABITS OF AMPULLARIA. 113 



(B.) Sinking Slowhj. — With all the soft parts well-protruded, or only 

 slightly retracted. Not a single bubble is given ofE. 



(C.) Craivlincj. — All the soft parts normally extended, and no air-bubbles 

 given off. 



III.- Re-Ascending by Means of Crawling. 



(A.) Up hard objects. — Body normally extended. 



(B.) Up fragile stems or leaves. — A sort of acrobatic progression, carried 



out with the greatest deliberation. Body extraordinarily spread 



out. 



Judging from the massive nature of the animal's body, one or two ex- 

 planations seem at first sight necessary to interpret its widely-diverging 

 modes of locomotion : (A) the animal is able to determine its pneumatical 

 adjustments at particular levels of the water, by secreting the needed amount 

 of air from its own tissues, or (B) it is able to inflate itself with the required 

 quantity, deriving it from either (a) the air which is found dissolved in the 

 water, or (b), the atmospheric air above the water-level. But when closely 

 examined in the light of facts, both of these suppositions fail. For if (A) 

 and (B), (a) were true, it is hard to understand why the animal is not able to 

 float to the surface, but tries to reach it by laboriously crawling up the 

 inner side of the aquarium, or up the plants that may be living in it. 

 (B) (b) breaks down, if we keep in mind the fact that when slowly sinking 

 to the bottom, there is neither the retraction of soft parts, nor the 

 extrusion of bubbles of air, which this theory requires. Thus, it can be 

 shown that a hypothesis which accounts for one set of facts, does not hold 

 good for the other. Another strange fact to crown the confusion with 

 regard to both (A) and (B), is that the animal is unable to float on the under- 

 surface of the water as Bijthinia and Lymnaea are capable of doing. We 

 see, therefore, that the whole phenomenon of Ampullarian locomotion, 

 from the firm adherence of its foot to smooth surfaces, and its slow but 

 steady progression at the surface of the water, down to its mysterious want 

 of power to float to the surface of the pond or aquarium, suggest a series 

 of problems in zoo-mechanics which need thorough investigation. The 

 subject is one also, that does not seem to have been taken up by any of those 

 specialists, who have made the subject of animal mechanics their particular 

 study. 



