516 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



Platk XXVII. 



Fig. 15. Section of egg ofBabamau variety of Alpheux heterocheUs in typical yolk pyramid stage 

 Sixty- four cells present, x 70. 



Fig. 16. Segmentation nucleus of egg of A. saulcyi, nearly central in jiositiou. x277. 



Fig. 17. Section of an egs of A; saulcyi, which was normally laid but unfertilized, .showing the 

 female pronucleus. x70. 



Fig. 18. Degenerating nuclei containing spore-like bodies, from the egg-nauplius 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 Astamis 

 fuviatiUs. After Keichenbach (54) Taf. viii, Fig. 67. This is taken from the egg- 

 nauplius stage to show the origin of " secondary mesoderm." The elements here 

 marked 7h', k are described as cells which have originated from the endoderm, aud 

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

 pared directly with b, Fuj. 18, and s, s^, Fig. 21, from the egg-nauplius of Alpheus 

 saulcyi, 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 oi Alpheus saulcyi, to 

 show the degenerative cell products. x610. 



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REFERENCE LETTERS. 



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

 Ch., chitioous egg membranes, 

 ec, ectoblast. 



»., nuclear body, with vesicular chromatin mass. 

 Ic, i', Ij m, m'-3, nuclear products in yolk. 

 Mes., mesoblast. 



N., NJ, nuclei of eutoblastic cells. 

 n., nucleolus of entoblascio cell (not clearly shown). 

 01., oil drop. 



Bet., protoplasmic reticulum. 

 S, 8, e^., degenerative products. 

 Sep., cleavage plane. 

 Std., foregut. 

 Vac, yolk vacuole, 

 r., yolk. 



¥. P., yolk pyramid. 

 T. S., yolk sphere. 



