On the ovogenesis and spermatogenesis of Sagitta bipunctata. 939 
and fewer granules outside of the nuclear-membrane. B & L., obj. '/,, 
oe, C. 
Figs. 13a—i. A series of chromosomes taken from oocytes of dif- 
ferent ages to show the gradual reduction in size. B. & L., obj. 1/,, 
oc. C. 
Fig. 14. Section of a nucleus in a stage between those of Figs. 11 
and 12. Here the chromosomes were all in the center of the nucleus 
in two sections, the nuclear plasm seemed filled with minute dark 
granules, and only a few granules were outside. B. & L., obj. '/,, 
oc. C. 
Fig. 15. One whole chromosome, and parts of two others, similar 
to Fig. 13e, showing large granules, or nucleoli, B. & L., obj. 1/, 5, 
oc. C. 
Fig. 16. Section through the two accessory cells of a nearly ripe 
oocyte, showing the connection with the spermduct, the spermhead in 
the second accessory cell, and the micropyle-like opening in the egg- 
membrane, where the formation of the membrane was prevented by 
the presence of the accessory cells. B. & L., obj. 1/,,, oc. C. 
Figs. 17—18. Earlier stages showing the relation of the accessory 
cells to the oocyte, and the formation of the opening for the entrance 
of the spermatozoon. 
Pilate Qa: 
The figures in this plate were all drawn with camera, and Zeiss 
objective 1,5, oil-immersion; ocular 8. 
Fig. 19. Section of a group of spermatocytes just breaking loose 
from the testis, showing resting nuclei; a cross-section (a) of the 18 
rod-shaped chromosomes at one pole of a division spindle; and one cell 
in division (b), where the chromosomes appear in reduced number as 
loops at the poles of the spindle. 
Fig. 20. 18 rod-shaped chromosomes at one pole of the spindle 
of a dividing spermatogonium. 
Figs. 21—22. Longitudinal sections of spermatogonia spindles 
showing only a few of the chromosomes. 
Fig. 23. Chromosomes in loop-form, from a stage similar to that 
of Fig. 1b. 
Fig. 24—25. Growth stages in which nine regularly disposed, 
deeply-staining loop-shaped chromosomes appear. 
Fig. 26. Cross-section of a cell like those of Fig. 25, showing 
18 sections, two belonging to each chromosome. 
Fig. 27. A later stage in which the chromosomes stain less 
deeply. 
Fig. 28a. A still later growth stage in which the chromosomes 
are only faintly visible; b a later stage in which the chromosomes 
appear as shortened loops or V’s, and again stain very deeply. 
