Germ Cells and early Embryology of certain Aphids. 639 
Explanation of plates. 
Plate 49. 
1. The spireme stage of the last ovogonial division. 
2. The division of spireme in the formation of chromosomes. 
Fig. 3—4. Formation of chromosomes, 4 large, 2 small. 
g. 5—8. The last ovogonial division. 
Fig. 9. 
Fig. 10—11. Beginning of the growth period and appearance of 
chromosomes. 
Fig. 12. Cross section of the distal end of the end chamber with 
ovum at the time of its entrance into the oviduct. 
Polar view of last ovogonial division. 
Fig. 13. Long section of ovum, showing the distinct germinal vesicle 
membrane and the granular appearance of the chromatin. y.s yolk spheres. 
Fig. 14. Ovum showing nucleus in synapsis. 
Fig. 15. Long. section of part of an ovum showing condition of 
germinal vesicle in center, at the end of the growth period. pr periplasm, 
y. s yolk spheres. 
Fig. 16—17. Section of germinal vesicle only, showing condition of 
nucleoplasm and the formation of the chromatin spireme. nel nucleolus. 
Fig. 18—19. Division of spireme and formation of chromatin rod 
or chromosomes. 
Fig. 20. Longitudinal splitting of chromosomes. 
Fig. 21. Long. section of ovum at the time of the formation of the 
first polar body. pb, first polar body, nel nucleolus. 
Fig. 22—23. Condition of ovum after the formation of the second 
polar body. pb, second polar body, prn pronucleus. 
