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COMMON REFERENCE LE^FPERS USED IN THE FIGURES. 



a, anterior end of tbe blastoderm. 



ac, arcbenteric cavity. 



ft, blastopore. 



ce, individualizing cells. 



d, dorsal lip of tbe blastopore. 



c, invaginated or gut-entoderm. 



E, region covered by gut-entoderm. 



cc, ectoderm. 



gw, germ-wall. 



m, yolk masses. 



np, Nucleus of Pander. 



0, region of overgrowtb. 



p, posterior end of tbe blastoderm. 



pn, periblastic nucleus. 



s, segmentation cells. 



sc, segmentation cavity. 



sg, subgorminal cavity. 



3, zone of junction. 



