522 MEMOlltS OF TUE NATIONAL ACADEMY OF SCIENCES. 



PLATE XXX. 



FIG. 37. Part of section of egg before iuvaginatioii stage, showing primary yolk cells. All the 



figures ou this plate, excepting Fig. 46, refer to the Babamau form of Alpheus hetero- 



cheUn. x277. 

 KM;. 38-44. Consecutive 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. x70. 

 FIG. 45. Section through the same egg, showing sernidiagramrnatically tjhe structure of the yolk. 



X70. 

 FIG. 40. Section through the egg of A. .mi/lci/i at a slightly later stage, but before iuvaginatioii. 



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 occurred below the surface, x 70. 

 KM;. 47. Surface view of the side of egg, corresponding to the germinal area in nearly the same 



stage. X70. 

 KM;. IS. Tangential section, showing blastodermic cells of same egg. x277. 



REFERENCE LETTERS. 



ii. a' 7 . L't'lls migrating from blastoderm into the yolk. 



I'.il. I'., blastodermic cell. 



Ch., eggshell. 



G. D., embryonic area. 



Sep., yolk cleavage plane. 



1'. ., yolk ball. 



