516 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



PLATE XXVII. 



FIG. 15. Section of egg of Baliaimin variety of Alpheun heterochelis in typical yolk pyramid stage 

 Sixty- four cells present, x 70. 



FIG. 16. Segmentation nucleus of egg of A. sauleyi, nearly central in position. x277. 



FIG. 17. Section of an egg of A. sauleyi, wbich was normally laid but unfertilized, showing the 

 female pronucleus. x70. 



FIG. 18. Degenerating nuclei containing spore like bodies, from tlie egg-uauplius embryo, the 

 structure of which is shown in Pis. XLI-XLIII. x610. 



FIG. 19. Blood cells of adult Alpheus. x 610. 



FIG. 20. Endodermal cells from the ventral wall of the primitive alimentary cavity of Astacus 

 fluviatilis. After Reicheubnch (54) Taf. Vin, Fig. 67. This is taken from the egg- 

 uauplins stage to show the origin of " secondary mesoderrn." The elements here 

 marked ', A- are described as cells which have originated from the eudoderm, and 

 completed their metamorphosis into ordinary mesoderm cells. These may be com- 

 pared directly with b, FIG. IS, and s, s~, Fig. 21, from the egg-uauplius of Alpheus 

 sauleyi, and are rather to be regarded as nuclear bodies in the earlier stages of 

 retrogressive metamorphosis. x256. 



FIG. 21. Part of transverse section through the foregut of the egg-nauplius of Alpheus sauleyi, to 

 show the degenerative cell products. x610. 



REFERENCE LETTERS. 



A. T.S., altered food-yolk. 

 Ch., chitiuous egg membranes. 

 ec., ectoblast. 



i., nuclear body, with vesicular chromatin mass. 

 k, k 1 , I, m, m 1 " 3 , nuclear products in yolk. 

 Mes., mesoblast. 



JV., JV. 1 , nuclei of eutoblastic cells, 

 n., uucleolus of cntoblastic cell (not clearly shown). 

 01., oil drop. 



Bel., protoplasmic reticulum. 

 S, s, a-., degenerative products. 

 Sep.', cleavage plane. 

 Std., foregut. 

 Vac. , yolk vacuole. 

 r., yolk. 



T. P., yolk pyramid. 

 Y.S., yolk sphere. 



