EXPLANATION OF PLATE II. 



A miiiiber in brackets refers to the figure from which the cells have been 

 enlarged. 



Fig. 1. Surface view of posterior end of an egg 2l^ hovu's after deposition. 

 The pole-disc occupies about % of the entire area. Only those yolk-globules 

 adjacent to the pole-disc are shown, a, circumference of egg indicated by 

 single line. X 200. 



Figs. 2 to 4 represent portions of the posterior end of eggs in longitudinal 

 section showing the arrangement of the pole-disc granules, x 850. 



Fig. 2. Egg taken from the oviduct of Leptinotarsa. Granules of pole-disc 

 are here very close together forming a broken strand. 



Fig. 3. Egg 13 hours after laying. This egg contained about 133 nuclei. 

 Granules of pole-disc suspended in the inner stratum of the "Keimhautblastem" 

 forming a network. 



Fig. 4. Egg 11 hours after laying. Pole-disc granules widely separated from 

 one another. 



Figs. 5 to 11 represent longitudinal sections through the posterior end (except 

 figure 8) of eggs, showing early stages in pole-cell formation. Granules of pole- 

 disc represented by dots, x 60. 



Fig. 5. One of the 4 pole-cell antecedents (a) is shown in this figui-e. 



Fig. 6. Three of the nuclei (a) in this figure divide once giving rise to 

 pole-cells. 



Fig. 7. The three nuclei indicated at a will become pole-cells. 



Fig. 8. Longitudinal section through an egg in Stage A. Seven pole-cell 

 nuclei are protruding from the posterior end of the egg. 



Fig. 9. Three of the six pole-cell nuclei represented in this figure have 

 entirely separated from the egg. 



Fig. 10. Blastoderm completed. Pole-cells form two layers. 



Fig. 11. Pole-cells form an irregular group, a, pole-cell in anaphase of 

 division. 



Figs. 12 to 15 represent surface views of the posterior end of eggs, showing 

 successive stages in pole-cell formation, x 200. 



Fig. 12. The four nuclei (a) under the center of the pole-disc will give rise 

 to all of the pole-cells. 



Fig. 13. Eight pairs of pole-cell nuclei may be recognized by their dark 

 granules. Eleven of the blastoderm-cell nuclei (a) contain a few pole-disc 

 granules, b, strand of cytoplasm connecting a pair of pole-cells. 



Fig. 14. Thirty-four pole-cells are present, each containing granules from the 

 pole-disc. One pole-cell (17) is in the late anaphase of mitosis. 



Fig. 15. Sixty-three pole-cells are visible. The blastoderm is fully formed. 



Fig. 16. Lateral surface view of the posterior end of egg in Stage B. Part 

 of the pole-cells occupy an Indentation in the end of the egg. The pseudo- 

 blastodermic nuclei appear as a dark mass in the interior, x 200. 



Fig. 17. Pole-cell in anaphase of mitosis. Enlarged from Fig. 14, position 

 17. The pole-disc granules have been equally distributed to the two ends of 

 the cell. X 850. 



