NUCLEOLI IN EUSCHISTUS VARIOLARIUS. 235 



PHOTO 13. A young germinal vesicle with thechromatin almost in a diffused con- 

 dition. A small, clear, spherical space is present, which may represent the first ap- 

 pearance of the achromatic nucleolus so conspicuous in the older germinal vesicles of 

 Photos 1 8 to 30. 



PHOTO 14. A young germinal vesicle with the chromatin evenly distributed as in 

 Photo II. 



PHOTO 15. An older germinal vesicle with the chromatin segregated into numerous 

 clumps as in Photo 12. Many of the clumps in this germinal vesicle appear almost as 

 dense as nucleolf, though in the preparation they are seen to be merely a close segre- 

 gation of fine granules. 



PHOTO 1 6. An older germinal vesicle showing less pronounced segregations of 

 chromatin, and a clear spherical space which can surely be interpreted as an early 

 appearance of the achromatic nucleolus seen in the germinal vesicles of Photos 1 8 to 30. 



PHOTO 17. A much larger germinal vesicle with the chromatin quite evenly dis- 

 tributed as granules. 



PHOTO 18. An older germinal vesicle with the first indication of the formation of 

 delicate chromatic threads, which later develop into the chromosomes. At this stage 

 the achromatic nucleolus is always present. The cracked spaces shown in this ger- 

 minal vesicle and in Photos 21, 23, 24 and 29 are due to uneven shrinkage as the 

 germinal vesicles rapidly dry on the slide. 



PHOTO 19. A much later stage than Photo 18 the chromatin threads being well 

 formed. (The next stage to Photo 18 is shown in Photo 20, Plate II.) The ger- 

 minal vesicle of this preparation is not well flattened and some of the chromatic 

 threads are very much out of focus. 



