No. I.] 



THE EMBRYOLOGY OF CREPIDULA. 



209 



Reference Letters. 



A. Left anterior macromere. 



B. Right anterior macromere. 



C. Right posterior macromere. 



D. Left posterior macromere. 



1(2, \b, \c, id, i«', etc. First quartette of ectomeres. 



2a, 2b, 2c, 2d, 2«', etc. Second quartette of ectomeres. 



3a, 33, 3<r, 3^/, 3a', etc. Third quartette of ectomeres. 



^A, 4B, 4C, 4D. Fourth quartette (Entomeres and mesomeres). 



SA, ^B, 5C, S-D- Fifth quartette (Entomeres). 



ME, ME, Me, Me. Mesentoblasts. 



M, M. Mesoblastic teloblasts. 



E. E, e, e. Enterobiasis (intestinal cells). 



