42 Overton . — On the O rganization of the Nuclei in the 
Popoff (’07), Paludina vivipara , Figs. 34 and 35 , PL V, Helix pomatia , 
Figs. 88 - 91 , PI. VIII. 
The studies of Harper (’05) and of Miss Sands (’07) on certain mildews, 
in which the chromatic strands are in continuous connexion with a per- 
manent central body, furnish conclusive direct evidence that the chromosomes 
are permanent cell structures in these plants. 
As the result of a series of experimental studies on Ascaris, Boveri (’04) 
has, perhaps, given the most complete statement of what he terms the 
Hypothesis or Theory of the Individuality of the Chromosomes’. He 
conceives the chromosomes as individual, elementary organisms, ‘ die in der 
Zelle ihre selbstandige Existenz fiihren ’, a conception which Rabl (’06) has 
also adopted. Harper (’05) points out that it is, perhaps, questionable 
whether Boveri is justified in combining the conception of the permanence 
of the chromosome and the doctrine that they are individual or elementary 
organisms, which lead a relatively independent existence in the cell. He 
further doubts if permanence in number, form, and position in the nucleus 
even suggests such a conclusion, any more than that the cytoplasm is an 
individual organization because it grows and divides. Apparently no more 
is gained in support of the hypothesis of chromosome individuality by 
regardingthe chromosomes as elementary, relatively independent organisms, 
which bear a symbiotic relationship to the cell than that they are definite 
permanent parts of a cell mechanism, having a permanent but not necessarily 
independent existence in the cell. 
One of the strongest arguments of the individuality of the chromosomes 
is the fact that the size of the nucleus is dependent upon the number of 
chromosomes which it contains. Boveri (’05, ’07) has shown that in sea- 
urchin larvae the surface area is proportional to the number of chromosomes 
which the nucleus contains. In nuclei which contain an abnormal number 
of chromosomes, he also finds that the abnormal number prevails during the 
subsequent divisions. 
Nemec (’04) found that in chloralized roots of Pisum many cells 
contain large nuclei with twice or four times the normal number of 
chromosomes. Strasburger (’07) has repeated these experiments, and 
obtained similar results. He finds evidence that the quadruple number, 
once established, persists. Evidence that the number of chromosomes 
determines the size of the nucleus is also furnished in the development of 
supernumerary pollen grains and nuclei of certain plants especially hybrids, 
as has been found by Strasburger (’82) and Juel (’97) for Hemcrocallis , and 
by Cannon (’03), Tischler (’06, ’08), and others for certain plants. 
Results similar to those of Boveri, showing that the number of 
chromosomes determines the size of the nucleus, were obtained by Zur 
Strassen (’98) in the giant embryos of Ascaris. Boveri (’92, ’95) in his 
studies on fertilized enucleated eggs of Echinoderms showed that exactly 
