i i > i H ; \ 



they next be-ome iii"r.- di>tinet, as on July 7, fig. 20. Further, l.y ad 

 \.iii.ini: iiieivment, an elongated white shell occupies the whole - 

 within tli.- integumentary outline, as on July 17, fi^. '21. 



Tin- youiiu' attain maturity in about a month, or within u lew da\* 

 leas or more. Th<-y an- very minute, pure white, and, to th -\--. of a 

 Ion!: o\.d >}i ape. But under the microacope, they proveof a true regular 

 oval ; tin- animal irtvyi-li -drown, with its two black eyes distinct; mid 

 then there is evident pulsation of the heart. The margin of the shell at 

 tliat time li^ht-grey. spiva Is an oval border around its contents. 



II :. it may be observe.!, that the figures of originating part- i- 



1 'iy th.-ir tr;in-p.irence. A narrower or a broader oval on 

 iriilar ein-li', was determined more justly by the microscope than by t!i- 

 unarmed e\ 



Tlie>e animaU have bred from the beginning of June to the IM-L-UI- 

 iiini: of Aiii:ii>t. 



They aiv not so common as the preceding species. 



1'i.vTi; VI. 



1. Ancylut jlKciatilii, shell, upper surface. 



2. Animal in the shell, under surface, outline. 

 .3. Animal in the shell, slightly enlarged. 



4. Another specimen, under surface. 



5. Spawn consisting of two ova, September 27. 



6. The same, enlarged. 



7. The some, farther advanced, October 20. 



8. 9, 10. Spawn with ova in various number and arrangement. 



1 1 . Enlarged view of fig. 8. 



12. Spawn of August 23. 



13. The same, enlarp !. 



14. Nascent Ancylus from the preceding spawn, back of tin- xtu-ll 



Urged. 



15. Exterior of the empty shell of an Ancylus, enlarged. 



16. The same, more enlarged. 



17. Adult regenerating tin- inn.-r part of the shell in front, 



18. Anryltu lacuttri*, upper surface. 



19. The same, under surface. 



-. Spawn, on on July 7. enlarged. 

 21. The same, as on July 17, enlarged. 



