THE HISTORY OF THE CHROMOSOMAL VESICLES 



IN FUNDULUS AND THE THEORY OF GENETIC 



CONTINUITY OF CHROMOSOMES. 



A. RICHARDS, 



WABASH COLLEGE, CRAWFORDSVILLE, INDIANA. 



At the Columbus meeting of the American Society of Zoolo- 

 gists in 1915, the writer reported the occurrence of chromosomal 

 vesicles which could be recognized as persistent entities even in 

 the resting stage. Since that time it has been possible to trace 

 the history of these vesicles from the metaphase condition of the 

 chromosomes through the anaphase, telophases and the various 

 stages of interkinesis back to the prophase stage where the new 

 chromosomes are fully formed as new bodies which are as dis- 

 tinctly chromosomal in character as the more familiar ones of 

 the metaphase. This history can now be given with but few 

 gaps; and these are of comparatively little importance. The 

 bearing of these facts on the hypothesis of genetic continuity of 

 the chromosomes is direct and very important. 



The presence of persistent chromosomal vesicles was first 

 noted in the study of the eggs of Fundulus heteroclitus which 

 had been fertilized with the sperm of Ctenolabrus (Tautogoldbrus) 

 adspersus, and the history was first made out in a general way 

 upon those cleavage nuclei. Subsequently the observations were 

 extended to the Fundulus eggs fertilized normally by the sperm 

 of the same species, and the gaps in the series filled in from this 

 form. So far as could be determined there is no essential 

 morphological distinction in the figures presented by the normal 

 and the hybrid nuclei. The same account applies to both, 

 with the exception of certain points to be noted later, which do 

 not apply to the general facts and line of argument here given. 



The first observations were made while working on the hybrid 

 eggs to determine the effect of radiation upon the development, 

 particularly with the reference to the chromosomes which differ in 

 form and which can be recognized as distinct in the hybrid eggs as 



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