282 CALIFORNIA ACADEMY OF SCIENCES. [Proc. .^d Ser. 



EXPLANATION OF PLATE XXVII. 



Fig. 17. Progenetic stage of second mitosis. The cytoplasm shows a radial 



arrangement; in the region previously occupied by the spindle 



fibres of the first mitosis the cytoplasm is less dense. Granules 



which stain violet begin to make their appearance in strands 



of cytoplasm nearest the nucleus. 

 Fig. 18. Genetic stage. The violet granules gradually increase in number, 



become crowded, and fuse to form the genetic fibres. 

 Fig. 19. The genetic fibres increase in number and size. 

 Figs. 20 and 21. The genetic fibres increase and assume a more regular 



arrangement. The lower half of the figure shows in both cases a 



slightly more advanced stage than the upper. 

 Fig. 22. The upper half shows the genetic fibres fully formed; in the lower 



half they are assembling in groups to form the spindle cones; 



various stages in this process are shown. 

 Fig. 23. The upper half shows the cones fully formed: the lower half shows 



the breaking down of the nuclear wall and the penetration of the 



genetic fibres into the nucleus, marking the commencement of 



the stellar stage. 

 Fig. 24. The nuclear wall has completely disappeared; the chromosomes 



preserve their original arrangement. 



