CENTROSOMES IN THE ANNELID EGG. 213 
EXPLANATION OF PLATE XVII. 
With the possible exception of Figs. 14 to 16, all are fertilized. 
Fic. 14. First maturation-spindle after the disappearance of nucleoli. Double 
centrosome in each end. Circle of dots around end of spindle. (Two sections 
combined.) 
Fic. 15. Similar to Fig. 14; centrosomes of inner aster further apart; circle 
of dots more deeply stained. 
Fic. 16. Circle of dots not brought out, though the centrosomes are clear. 
There are probably two centrosomes at the outer end of the spindle, though only 
one shows in this section. 
Fic. 17. About ten minutes after fertilization. Daughter-chromosomes 
moving toward the pole of the spindle. The two centrosomes at the inner end 
of the spindle moving apart, showing a faint whitish band (not clear in the litho- 
graph) between them. 
Fic..18. Transverse section through the equatorial plate, showing the nine 
chromosomes. 
Fic. 19. First maturation-spindle in anaphase. Polar globule beginning to 
protrude. Young sperm-nucleus, ? with its single (?) centrosome. 
Fic. 20. The first polar globule. One of the outer centrosomes of the first 
maturation-spindle degenerating, but still visible. The two inner centrosomes 
widely separated, with an incipient spindle between them. A mere suggestion of 
a Zwischenkérper in the large spindle, z. The sperm-nucleus as in Fig. 19. This 
figure shows the distinction in color between the blue-black chromosomes and 
the brown-black centrosomes which is always present in the preparations them- 
selves. Sperm-nucleus from adjacent section. 
Fic. 21. Oblique view; first polar globule, Zwischenkérper, male pronucleus 
with aster and two centrosomes. Remains of centrosome in the polar globule. 
Combined from several sections. The full number (9) of chromosomes in the 
egg. 
Fic. 22. Oblique section; after the evanescence of the first maturation- 
spindle. Some of the chromosomes at inner end of the first spindle ; compare 
Fig. 20. The two centrosomes more widely separated, between them the incipient 
central spindle; Z.g., polar globule in tangential section. Two sperm-centro- 
somes. 
Fic. 23. Incipient second maturation-spindle ; slightly later than Fig. 22, not 
all the chromosomes in this section. 
Fic. 24. Two adjacent sectionsa and 4; /.g., first polar globule with chromo- 
somes fusing together ; second maturation-spindle far advanced. 
Fic. 25. Second maturation-spindle#beginning to swing around into vertical 
position. Sperm-nucleus with aster and two centrosomes. 
Fic. 26. The second maturation-spindle in its final position. Aster of sperm- 
nucleus with extensive rays. 
Fic. 27. Second maturation-spindle a little later. 
Fic. 28. Same, with quadruple chromosomes. Circle of dots around end of 
spindle; compare Figs. 3, 14, and 15. 
