DESCRIPTION OF PLATES. 



Letters of Reference. 



an. Anus. 

 a. s. Aortic sinus. 

 ait. Auricle. 



/. Foot. 



g. r. Rudimentary gill. 

 r. g. f. Rudimentary gill filament. 

 g. f. Gill filament. 



r. Fold that forms part of floor 



of lung. 

 //. 7'. Head vesicle. 



k. Kidney. 



/. r. Rudimentary lung. 

 /. g. Lung groove. 



/. Lung. 

 m. Mouth. 



;;;. c. Cavity of mantle. 

 in. f. Edge of shell gland. 

 n. Nerve tissue. 



resp 



oe. CEsophagus. 

 o. Operculum. 



o. r. Rudimentary osphradium. 

 osph. Osphradium. 

 part. Partition of cavity of mantle. 

 per. Pericardium. 

 />. J. Pulmonary sinus. 

 p. v. Pulmonary vein. 

 r. s. Radula sac. 

 ree. Rectum. 



. ntd. Rudiment of organs of respira- 

 tion. 



sh. Shell. 



sh. g. Shell gland. 

 p. st. Primitive stomach. 

 st. Stomach, 

 f. Velum. 

 ren. Ventricle. 



EXPLANATION OF PLATES. 



PLATES i TO /. 

 All of the figures are of AmpnUaria deprcssa Say. 



PLATE i. 



FIGS, i and 2. Adult, natural size. 



FIGS. 3 and 4. Enlarged view of shell at time of hatching. 



FIGS. 5 and 6. Enlarged view of shell of unhatched embryo 1.8 mm. long. 



FIG. "/. Surface view of an unhatched embryo 1.2 mm. long. 



FIG. 8. Eggs attached to grass. 



PLATE 2. 



FIGS. 9 and 10. Sections of the organs of respiration in their earliest stages. Figure 

 10 shows a stage somewhat older than that illustrated in figure 9. 



PLATE 3. 



FIG. II. Reconstruction from a series of oblique sagittal sections of an embryo in 

 the stage shown in figure "/, plate i. 



PLATE 4. 

 FIG. 12. Sagittal section of mantle-chamber and respiratory organs in an embryo 



1.2 mm. long. 

 FIG. 13. Transverse section of the mantle-chamber of an embryo 1.4 mm. long. 



PLATE 5. 



FIG. 14. Transverse section of the mantle chamber of an embryo 1.4 mm. long. 

 FIG. 15. Section of the respiratory organs at the time of hatching. 



PLATE 6. 



FIGS. 16 and 17. Section of mantle-chamber showing lung, gill, etc. Figure 16 shows 

 a stage wherein the embryo is 1.8 mm. long and is older than that shown 

 in figure i/. 



PLATE ~. 



Fi<;. 1 8. Section of an unhatclu-d embryo 2.1 mm. long. 

 104 



