522 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



Plate XXX. 



Fig. 37. Part of section of egg before iu pagination stage, showing primary yolk cells. All the 



figures on this plate, excepting Fig. 46, refer to the Bahainan form of Alphem hetero- 



chelift. X 277. 

 Fig. 38-44. Consecntive sections of the same egg, showing the progress of the primary yolk cells 



in their migration from the blastoderm to the central parts of the egg. x 70. 

 Fig. 45. Section through tlie same egg, .showing seinirtiagrammatically the structure of the yolk. 



X70. 

 Fig. 4C. Section through the egg of .1. saitlci/i at a slightly later stage, but before invagination. 



The blastodermic cells lie at the surface, the primary yolk cells toward the center of 



the egg. Traces of the primary yolk cleavage are still seen at the surface, and a 



secondary cleavage has pccurred below the surface, x 7(1. 

 Fig. 47. Surface view of the side of egg, corresponding to the germinal area iu nearly the same 



stage. X 70. 

 Fig. 48. Tangential section, showing blastodermic cells of same egg. x 377. 



REFERENCE LETTERS. 



a, o'~', cells migratinfi; from blastoderui into the yolk. 



Bd. C, blastodermic cell. 



Ch., eggshell. 



G. D., embryonic area. 



Sep., yolk cleavage plane. 



F. B., yolk baU. 



