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 betweén 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 depressa Say 
by Professor Wm. H. Dall. The shell of the adult is shown of the natural 
size in plate 1, figures 1 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 1 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. 
