PLATE 4 



EXPLANATION OF FIGURES 



19 Section through the middle of the body of a second larva 299.5 hours old 

 (figs. 8 and 17). 



20 Detail structure of germ cells from a larva 359.5 hours old. One germ cell 

 is cut through the nucleus, the other along one side. 



21 Section of a larva 373.5 hours old. The coelom is forming at this stage 

 on each side of the intestine. One germ cell is shown near the ventral mesentery. 



22 Section through the middle of the body of a larva 429.5 hours old. 



23 Section through the caudal region of a larva 429.5 hours old (same larva 

 as the preceding figure). The coelom is forming and a germ cell (g) is included 

 in the somatic layer of the mesoderm. 



24 Section through the middle part of the body of a larva 478.5 hours old. 

 The germ cell in the figure is at the cranial end of the germ-gland anlage. 



25 The germ cell in figure 26 greatly enlarged. It shows disintegration of 

 yolk globules and the elimination of chromatin-like material from the nucleus. 



26 Section through the middle of the body of a larva 538.5 hours old. The 

 yolk is beginning to disappear in the most cranial germ cells. 



27 Section through the germ-gland region of a larva 20 mm. long. The germ 

 ridge is forming and the germ cells are migrating into it. 



28 Enlarged drawing of two germ cells from the same larva as the preceding 

 figure, showing astrospheres and vitelline bodies. 



29 Section of a larva 11 mm. long in the region of the germ gland. At this 

 stage the germ cells have lost their yolk. 



30 Enlarged drawing of the germ cells shown in figure 29. The germ cells 

 lie above the germinal epithelium and are not a part of it. There is no germ 

 ridge at this stage. 



31 A section of the intestine near its caudal end from a 10-mm. larva. The 

 lumen of the intestine is filled with cells that have been extruded. 



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