THE GERM-CELLS OF CICADA (TIBICEN) SEPTEMDECIM. 447 



cording to Delle Valle, chromosomes are not constant structures 

 of the cell and their number varies as ordinary fluctuating 

 variations, since the number in a particular cell depends upon 

 the mean size of the chromosomes, the amount of chromatin 

 in the nucleus being constant (McClung, '17, p. 548). I have 

 already (page 409) called attention to the remarkable difference 

 between the metaphase chromosomes of the young follicle-cells 

 and those of old follicle-cells (compare Figs. 7, 10, 11). In the 

 old follicle-cells, the chromosomes are somewhat longer, thinner 

 and poor in chromatin constitution. The nuclei from which such 

 chromosomes are derived are much poorer in basichromatin 

 than the nuclei of the young follicle-cells, usually having only a 

 single small mass of basichromatin. Nevertheless, as will be 

 seen from Figs. 10 and n, the chromosome number remains 

 constant and their relative sizes are similar to the chromosomes 

 of other diploid groups; their only difference seems to be that 

 they possess less chromatin. It is at once evident that this 

 condition cannot be interpreted on the basis of Delle Valle's 

 hypothesis. It also brings to light the fact that the material 

 concerned in maintaining the chromosome number and size is 

 not the chromatin of the nucleus, which is apparently more 

 or less variable in amount, but the underlying structural basis 

 of the chromosomes, namely the linin. In a previous paper 

 (Shaffer, '20), I have emphasized the importance of the linin as 

 being responsible for the architecture and organization of the 

 chromosomes and for the maintenance of the stability of the 

 nuclear elements. The chromomeres of the chromosomes are 

 linearly arranged in a definite order (Wenrich, '16) which is 

 maintained constant through the agency of the linin, the struc- 

 tural basis. Besides this, the linin is also concerned in the 

 movements and localization of the chromatic elements of the 

 nucleus. Some of the most fundamental problems of the cell 

 are bound up with such phenomena, namely, w r hat determines 

 how the chromomeres shall be arranged in the chromosome, or 

 by what agency are homologous chromosomes brought together 

 in synapsis. "As long as 'conjugation' of the chromosomes is 

 dealt with as though they were entities with independent power 

 of movement, instead of the processes back of it, the super- 



