The Origin of the Lung of Ampullaria. 103 



which is shown in plate I, figures 3 and 4. The lung is deeply infolded and 

 the section cuts nine gill-filaments, g. f. 



Plate 5, figure 15, is from a young Ampullaria, at the time of hatching, 

 with its organs of respiration in their definitive adult condition. The lung, 

 I, is now a spacious chamber occupying most of the thickness of the mantle 

 and opening into its chamber by a small, closable aperture. 



At about this time the gill and the lung become separated from each 

 other by a valvular fold (part} which grows out from the body into the 

 chamber of the mantle. 



Summary. The gills, the lung, and the osphradium of Ampullaria 

 arise simultaneously, or nearly so, in the embryo; and they are developed 

 out of a ridge or thickening of the epithelium of the mantle. They must, 

 therefore, be regarded as a series of homologous organs specialized among 

 themselves in different directions, and not as independent acquisitions. 

 There is no reason to think that there is any ancestral connection or rela- 

 tionship between the lung of Ampullaria and that of the pulmonates, 

 although the embryonic history of the lung of Ampullaria shows that the 

 origin of the lung of the pulmonates through the modification of a gill, 

 or part of a gill, is not impossible. The lung of Ampullaria becomes func- 

 tional before the gill does ; for the newly hatched young die very quickly 

 if they are prevented from leaving the water, while the adults survive a 

 long immersion. 



LITERATURE. 



A. BAVAY. 



Au sujet d'un petit groupe de mollusques pulmones terrestres opercules, pourvus 

 d'un canal aerifere loge dans le test. Bull. Soc. Z. France, tome xxvm. 1903. 

 R. v. ERLANGER. 



Zur Entwicklung von Paludina vivipara. I u. II Theil. Morphol. Jahrb., Bd. xvm, 



Heft. 3. 1891. 

 H. OTTO und C. TONNIGES. 



Untersuchen iiber die Entwicklung von Paludina vivipara. Zeit. fiir wis. Zool., 



Bd. xvm, Heft. 3. 1906. 

 QUOY et GAIMARD. 



Voyage de L'Astrolabe, tome in. 1834. 

 V. V. RAMANAN. 



On the respiratory and locomotory habits of Ampullaria globosa Swainson. Jour. 

 Mai. London, vol. x. 1903. 



