HISTORY OF CHROMOSOMAL VESICLES IN FUNDULUS. 279 



behavior as a more thorough-going knowledge of the latter is 

 obtained. It is a noteworthy fact that those cases where 

 heredity does not seem to conform to the expectation based upon 

 the behavior of chromosomes are usually cases where the chromo- 

 somes are small, numerous and imperfectly known, and that in 

 general the difficulties in comparing the two sets of facts have to 

 a large extent disappeared with increasing knowledge. 



The significance of hybridization experiments for the doctrine 

 of chromosome continuity has been repeatedly pointed out, and 

 a single case will serve to illustrate it. Federley crosses different 

 species of the moth Pygcera in which the diploid and haploid 

 chromosome numbers are as follows: P, anachoreta, sixty and 

 thirty; P. cur tula, fifty-eight and twenty-nine; and P. pigra, 

 forty-six and twenty-three. In whatever cross was made of 

 these three species the chromosome number of the hybrid was 

 the sum of the two haploid sets that went in. According to 

 Federley the chromosomes preserve their continuity through 

 many generations of foreign cytoplasm. 



Evidence that there is chromosome continuity in plants is 

 quite abundant, as may be seen for example, from the reviews of 

 Stout and of Wenrich. Only the main trends of the evidence 

 need be mentioned here. First of these are the findings of 

 Rosenberg, Overton, Lundagard and others that in the somatic 

 cells of a considerable number of plants there occur in the resting 

 nuclei chromatic bodies of the same number as the chromosomes 

 during metaphase: these bodies enlarge directly into the prophase 

 chromosomes. To certain other types of plant nuclei the views 

 of Gregoire and his school apply. According to this idea the 

 chromosomes as they pass to the poles become vacuolated, or 

 alveolized, often forming in the resting nuclei reticulate bands 

 which later are transformed into a spiral thread, the prophase 

 chromosome of the next division. Of especial interest because 

 of the very suggestive similarity of the method by which chromo- 

 somes are formed in Fimdulus, is the view of Bonnevie resulting 

 from the study of both plant and animal cells, Allium and Ascaris. 

 She believes that there is genetic continuity of chromosomes al- 

 though there is no identity between those of different mitoses: 

 from the substance of each chromosome at the end of its life 



