EXPLANATION OF PLATE III. 



Fig. 18. Two nuclei which will give rise to four pole-cells ; enlarged from 

 Fig. 6, position 18. a, boundary between nucleus and cytoplasm ; b, chromo- 

 somes partiallj^ arranged in equatorial plate. X ^50. 



Fig. 10. Two nuclei which will become pole-cells; enlarged from Fig. 7, 

 position 10. a, pole-disc granules accumulated in compact mass. Compare 

 pole-disc in Fig. 2. X 850. 



Fig. 20. Two pole-cell nuclei (a and b) and one blastoderm cell nucleus (c) ; 

 enlarged from Fig. 8, position 20. d, pole-disc granules which remain in 

 "Kelmhautblastem" after the pole-cells are protruded. X 850. 



Fig. 21. One pole-cell nucleus enlarged from Fig. 9, position 21. The pole- 

 disc graniiles entirely surround the nucleus, x 850. 



Figs. 23 to 27 represent longitudinal sections of portions of the posterior 

 end of eggs, showing the arrangement of the pole-cells, and the formation of 

 the pseudoblastodermic nuclei and the pole-cell canal, x 200. 



Fig. 23. Blastoderm ends abruptly where it encounters the pole-cells, a, 

 pole-cell in anaphase of mitosis. 



Fig. 24. A few blastoderm-nuclei have been pushed upward past the pole- 

 cells into the yolk to form pseudoblastodermic nuclei. 



Fig. 25. Pseudoblastodermic nuclei now form a funnel shaped syncytium 

 just above the pole-cells. 



Fig. 26. In this figure (Leptinotarsa) the pole-cells are larger and have 

 larger nuclei than the blastoderm-cells. A few pseudoblastodermic nuclei 

 (ps.bl.n.) are present. 



Fig. 27. The pole-cells in C. lunata here show an arrangement similar to 

 those in C. multipunctata (Fig. 24). a, one pole-cell in tlie last stage of 

 division. 



Fig. 28. A pole-cell and an adjacent blastoderm-cell enlarged from Fig. 25, 

 (28). X 850. 



Figs. 29 to 32 represent surface views of eggs showing how the group of 

 pole-cells is carried into the posterior amniotic cavity. X 50. 



Fig. 29. A'entral view (Stage E). A shortening of the germ-band has 

 carried the pole-cells into the posterior depression of the ventral groove. 



Fig. 30. Lateral view of same egg as Fig. 29. a, cephalic lobe of germ- 

 band ; b, invagination which will give rise to the stomodeum. 



Fig. 31. View of posterior end of same egg as Fig. 29. 



Fig. 32. Ventral view (Stage F). Pole-cells, partly covered by lateral 

 folds, lie in the posterior depression of ventral groove (a). This depression 

 is now the posterior amniotic cavity. 



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