HISTORY OF CHROMOSOMAL VESICLES IN FUNDULUS. 259 



not normally coalesce, these resting nuclei gave additional cred- 

 ence to the belief that the vesicles maintain themselves over the 

 resting stage as separate entities. Subsequent observations on 

 the prophase render this position indisputable. (See below in 

 connection with Fig. 22.) Careful study under very high power 

 with proper conditions of lens definition and illumination on 

 well fixed material leave very little doubt that the vesicles do 

 remain separate. It is true that a one-to-one correspondence 

 cannot be established between the number of vesicles in the rest- 

 ing stage and the number of chromosomes in the metaphase 

 plate. This is true for two reasons: it is not possible to count 

 with accuracy the number of these chromosomes when they 

 are most condensed and therefore have the sharpest outline; 

 and it is even more impossible to count the number of vesicles, 

 for the plane of the section usually passes through some of them, 

 and it is too uncertain to attempt to superimpose the vesicles 

 of one section on those of the other to make a count, while at 

 the same time all of the vesicles cannot be seen in a preparation 

 of the nucleus as a whole. The inability to count the number of 

 vesicles, however, is hardly an argument against their permanence 

 for the reason that they can be followed through the interkinesis 

 and prophases as is shown in the later figures. 



These observations on the method of the reconstruction of 

 the nuclei have a certain bearing on the problem of the nature 

 of the nuclear membrane. Here, at least in its origin, the mem- 

 brane is formed of the outer walls of the chromosomal vesicles. 

 It may well be that the nuclear membrane of the resting cell is 

 more complex than this, due to the interaction between nucleus 

 and cytoplasm; indeed, some hold that the outer part of the 

 membrane is of cytoplasmic origin, and is therefore more of an 

 inner limiting membrane to the cytoplasm than of a constituent 

 part of nucleus. The writer sees evidence for this view on 

 Figs. 24 and 25 where more or less of the nuclear membrane still 

 remains, although the inner vesicular walls have broken down 

 and the new chromosomes have already formed. 



Nuclear membranes of the Fundulus type which are really the 

 outer vesicular walls find a parallel in the membrane formation 

 around single chromosomes which have become abnormally 



