Gross Anatomy of Campeloma. 



493 



than are those in the rear portion of the sac. All the young in 

 the anterior portion possess shells. The shell of the young at 



FIG. 2. 



this stage is devoid of colored epidermis, is crystalline white, and 

 possesses from 2 to 2J complete whorls. The apex is very short 

 and blunt, the first whorl being nearly uniform in diameter 

 throughout its length, while the body whorl is very large, com- 

 prising fully nine-tenths the entire bulk of the shell. The darker 

 tentacles and the black eyes at their outer base are readily seen 

 through the substance of the shell. The average dimensions of a 

 dozen or more young examined were, for length 3.5 mm., for 

 diameter 2.96 mm. The embryonic whorls never, so far as exper- 

 ience goes with mature specimens with completely preserved 

 apices, acquire the characteristic green epidermal coloring. 



