THE ORIGIN OF THE LUNG OF AMPULLARIA. 



]->Y \\ T . K. BROOKS AND BARTGIS MCGLONE. 



INTRODUCTORY. 



One of the authors was able to visit and partially explore the Everglades 

 of Florida, in March, 1906, through the courtesy of the Director of the Ma- 

 rine Biological Laboratory of the Carnegie Institution of Washington, Dr. 

 Alfred G. Mayer, in whose company the expedition was made. As we 

 pushed our way through the tall reeds and grasses that cover the shallow 

 water of the Everglades, we found great numbers of small eggs attached 

 to the stems, above the surface of the water, but close to it (fig. 8, plate i). 



The eggs are arranged in vertical rows and inclosed in calcareous shells, 

 resembling, in this respect, the eggs of the terrestrial pulmonate gasteropods. 

 We also found, in the water, the prosobranchiate gasteropod, Ampullaria, 

 in great abundance, and when some of the older eggs were opened, they 

 were found to contain young ampullarias. The Paludinidae, which are 

 closely related to the Ampullaridae, are aquatic, viviparous, and breathe by 

 gills ; and their structure seems to indicate that they are true prosobranchs, 

 descended from, and closely related to, the marine prosobranchs. Ampul- 

 laria has gills, is partially aquatic, and seems to be a true prosobranch ; but 

 as it has a lung, and is able to breathe air and live out of the water, and 

 as it also lays, in the air, eggs with calcareous shells like those of the terres- 

 trial pulmonates, the question whether it, and the Paludinidse, are primarily 

 pulmonates with secondary resemblances to the prosobranchs, or primarily 

 prosobranchs with secondary resemblances to the pulmonates, suggests itself. 

 As the embryonic history of the organs of respiration may be expected to 

 throw light upon this question, a quantity of eggs was collected and taken 

 to the Marine Laboratory in the Tortugas. There the eggs were opened, 

 the embryos removed, sketched and studied, and then hardened and pre- 

 served for more thorough examination. 



Sections show that the lung is a member of the series of gill-filaments, 

 and it must be regarded as a modified filament, or more than one. It is, 

 therefore, a secondary acquisition which is not derived from the lung of 

 the pulmonates. 



Both lung and gill arise very early, and simultaneously, in the embryonic 



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