Xidification and Emhryological Development 27 



Xo. 1. lOeggs, cap,'*ule3.5by2.5 mm. Xo. 8. 11 eggs, capsule 4.5 by 3.5 mm. 



2. 6 eggs, capsule 3.5 by 2.5 mm. 9. 2 eggs, capsule 4.5 by 2.5 mm. 



3. 8 eggs, capsule 3.0 by 3.0 mm. 10. 9 eggs, capsule 5.0 by 3.5 mm. 



4. 10 eggs, capsule 5.0 by 3.0 mm. 11. 5 eggs, capsule 4.5 by 3.5 mm. 



5. 4 eggs, capsule 3.5 by 2.5 mm. 12. 13 eggs, capsule 5.0 by 4.0 mm. 



6. 10 eggs, capsule 4.5 by 3.5 mm. 13 14 eggs, capsule 5.0 by 3.5 mm. 



7. 10 eggs, capsule 5.0 by 3.0 mm. 



Egg capsule No. 3 with eight eggs developed as follows: 

 March 13. Freshly deposited capsule. March 22. Embryo with shell of about one 



14. Early segmentation. whorl. 



15. Gastrula stage. 23. Embryo with shell half filling 



16. Gastrula and trochophore egg. 



stages. 24. Embryo with shell three- 



17. Gastrula and trochophore fourths filling egg. 



stages. ■ 25. Embryo with shell almost 



18. Trochophore and preveliger filling egg. 



stages. 26. Embryo with shell filling egg. 



19. Veliger stage. 27. Four efnbrv'os hatched. 



20. Early embryo stage. 28. Last embryo hatched. 



21. Embryo stage. 



The period of development was fifteen days. 



Capsule Xo. 6, with ten eggs, occupied a longer period (18 daj's) in 

 hatching. 



Capsule Xo. 8, with eleven eggs, had all embryos hatched in seventeen 

 days, from ]March 15 to ]\Iarch 31. Capsule X"o. 11, with five eggs, de- 

 veloped and hatched the young snails in thirteen days, from ^Nlarch 15 to 

 ^Nlarch 27. All other capsules occupied fifteen to eighteen days. The shell 

 when the young are hatched measures about 1.0 by 0.7 mm. 



About two weeks later (iVpril 2) six capsules were deposited measuring 

 as follows (see plate 52, figs. 2, 3) : 



Capsule 4.5 by 3.0 mm. with 10 eggs. Capsule 5.0 by 3.0 mm. with 9 eggs. 



Capsule 5.5 by 3.0 mm. with 7 eggs. Capsule 5.0 by 3.0 mm. with 19 eggs. 



Capsule 6.0 by 4.0 mm. with 14 eggs. Capsule 5.0 by 3.0 mm. with 9 eggs. 



One capsule with nine eggs developed as follows, the process occupying 

 but twelve days : 



April 2. Freshly deposited eggs. April 8. Post^•eliger and earlj' embrj'O 



3. Segmentation. stages. 



4. Segmentation and gastrula 9. Embryo with .small shell. 



stages. 10. Embryo filling egg. 



5. Gastrula and trochophore stages. 11. Embryo filling egg. 



6. Posttrochojihore and preveliger 12. Embryos hatching. 



stages. 13. Young snails all hatched. 



7. Preveliger and veliger stages. 



On ^May 22 the aquarium was examined for its entire contents. There 

 were ninety-six young snails of scalare only sixteen of which were living. 

 There were three adult specimens measuring 8 to 10 mm. in length. These, 

 curiously enough, were in shape more like Helisoma duryi seminole than 

 typical scalare. The shells were very wide with broad spire and decided 

 umbilicus. The young snails in the aquarium were approximately seven 

 and one-half weeks old. A few of these were measured and the number of 

 whorls was counted: 



Height 2.0; diameter 2.5 mm. Whorls 2. 



Height 3.0; diameter 3.0 mm. Whorls 2^>. 



Height 2.5; diameter 2.8 mm. Whorls 21/2- 



Height 2.5; diameter 2.8 mm. Whorls 21/4- 



