158 



BREATHING OF AMPULLARIA 



CHAP. 



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. Qb). 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 sec- 

 onds, 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 



^'"a^n "o^T" tteaZ'^ branchial cavity by the siphon and pass 



water; B, breathing air ; Si, OUt by the short right siphou. Some- 



Tnt^iU; ■x,^Sia/'e!7an- ^mes the animal remains under water 

 sion, performing the part of for hours without rising to the surfacc 

 SeTan/Lt^r, .'T "^ i^^pi^e 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 correspond- 

 ing position on the right side is a long filiform appendage, which 

 some have regarded as representing the other branchia. 



Opisthohranchiata. — A true branchia occurs only in the Tecti- 

 branchiata and the Ascoglossa. It lies on the right side, and is 

 usually more or less external, being partly covered sometimes 

 by the shell (as in Umbrella, Fig. 5), sometimes by a fold of the 

 mantle. In the Pteropoda (which are probably derived from 

 the Tectibranchiata), all the Thecosomata, with the exception 

 of Oavoli7iia, have no specialised branchia, but probably respire 

 through portions or the whole of the integument. In the Gym- 

 nosomata an accessory branchia has in many cases been devel- 

 oped at the posterior end of the body. Pneumodermon alone has 



II 



