HISTORY OF CHROMOSOMAL VESICLES IN FUNDULUS. 255 



exists as a mass contained in the sheath. Conklin has described 

 a similar structure for Crepidula chromosomes which consist of 

 "chromatin enclosed in a linin sheath." Figs. 4 to 7 show suc- 

 cessive steps in the anaphase and the various steps in the proc- 

 ess of vesicle formation. The chromomeres break up and the 

 granules of chromatin become peripherally arranged, and the 

 center is for a while free from granules. 



This central cavity of the chromosome does not seem to be a 

 definite vacuole, as is figured for instance in some plant chromo- 

 somes, but is simply the space within the walls filled in from 

 the fluid portion of the cytoplasm. The vesicle is achromatic 

 in its interior due to the superficial distribution of the chromatin. 

 Gradually there appear very fine strands or fibrils, doubtless of 

 linin, growing from the vesicle wall inward and the granules of , 

 chromatin which accompany them are particularly noticeable 

 at the intersection of the fibrils. Later the fibrils become 

 stronger and somewhat reticulated, while the granules on the 

 inner wall are farther and farther apart, and the vesicle is itself 

 in appearance a tiny nucleus in the typical resting stage. When 

 the reconstruction of the nucleus is complete, the granules are 

 small and fairly equally distributed and do not stain very densely. 

 At no time, however, does the nucleus become completely achro- 

 matic as is held in some cases. The behavior of the chromosome 

 during its reconstruction permits a very rough comparison to an 

 elastic bag tightly packed tightly with a fine granular substance. 

 As the bag takes in liquid it swells up and the non-soluble 

 granular substance becomes rolled up into tiny balls on the inner 

 surface, and occasionally chains of the granules extend into the 

 interior. 



This interpretation of the chromosome is not unlike Conklin's 

 view that these bodies consist of chromatin enclosed in a linin 

 sheath. As they move to the poles they- are transformed into 

 vesicles, the interior of which becomes achromatic, "though 

 frequently containing a nucleolus-like body, while the wall 

 remains chromatic. These vesicles continue to enlarge and 

 then unite into a 'resting nucleus'; the nuclear membrane is 

 composed of the outer walls of the vesicles, while the inner walls 

 stretch through the nucleus as chromatic portions." The 



