98 Papers from the Marine Biological Laboratory at Tortugas. 



history. In a young embryo, soon after the mantle is formed, a ridge or 

 thickening of the epithelium of its inner surface indicates the region where 

 the gill-filaments, the osphradium, and the lung are to arise. The osphra- 

 dium is developed from one end of this ridge, the gill-filaments from the 

 other, and between the two the ridge becomes infolded into the substance 

 of the mantle to give rise to the lung, which may be regarded as a modified 

 and invaginated gill-filament. The similarity of the lung to that of the pul- 

 monates is nothing more than a new illustration of resemblance between 

 organs that have been acquired independently under like physiological 

 conditions. 



DESCRIPTIVE. 



MATERIAL AND METHODS. 



The investigation that is here described is based upon the study of the 

 young stages in the development of an Ampullaria which occurs abundantly 

 in the Everglades of Florida. It is identified as Ampullaria dcprcssa Say 

 by Professor Wm. H. Ball. The shell of the adult is shown of the natural 

 size in plate I, figures I and 2; and at two early stages in figures 3. 4, 5, 

 and 6. Of these, 3 and 4 show the shell, enlarged, at the time when the 

 young mollusk leaves the egg, while that of a young embryo is shown, much 

 more enlarged, in 5 and 6. The eggs are laid, two or three inches above the 

 level of the water, on the stems of the reeds and grasses, in vertical rows 

 that are usually regular, as is shown in figure 8. Each is attached sepa- 

 rately by a tenacious cement or glue. They are inclosed in white, chalky, 

 calcareous shells. As the yolk is pink and, at first, fills the shell, while it is 

 shrunken and partially replaced by air in the older eggs, these undergo a 

 change of color during development, the younger ones being pink, while 

 the older ones are white. It is clear that the attempt to distinguish species 

 by separating ampullarias with pink eggs from those with white ones rests 

 upon a misconception. 



It is well known that Ampullaria has both gills and lung, and is adapted 

 for both aquatic and aerial respiration. The lung is a large, elliptical, thin- 

 walled pouch in the mantle, with an opening that is on the left side, above 

 the left siphon, and immediately posterior to the osphradium. It is well 

 shown in figures 5, 6, 7, and 8 of plate i of the Atlas of the Mollusca of 

 the Voyage de 1'Astrolabe. 



The series of embryos that afforded the material for this research is com- 

 plete, so far as the history of the respiratory organs is in question. In the 

 younger ones the shell is a thin, transparent flat cap, and there are no traces 

 of gills nor of lung ; and the collection includes an abundance of embryos 

 at each successive stage up to the time of hatching. 



The young mollusks were kept alive in captivity for four weeks or 

 more after hatching, but they did not undergo any observable change. 



