1 68 carrie i. woolsey. 



Discussion. 



McClung and others who have worked on the chromosomes of 

 the Orthoptera beheve there is a fixed or definite number for 

 each group of related insects, and presumably for all kinds of 

 life. Other writers disagree. Miss Browne ('13) has sum- 

 marized the work done and results obtained by many investiga- 

 tors on varied kinds of life so thoroughly that I shall not go into 

 this in detail. I shall, however, review the methods as set 

 forth by her whereby the changes in the chromosome numbers 

 have been accounted for by the various authors. 

 . One method is by the fusion or separation of particular chromo- 

 somes. Miss Browne in her work on Notonecta ('13) and Wilson 

 ('11) on Nezara use this explanation. A change in number by 

 a process of fusion was used by McClung ('05) and Robertson 

 ('15) in the appearance of a multiple chromosome, the former in 

 Hesperotettix and Mermiria, the latter in Chorthippus (Steno- 

 bothrus) curtipennis . A change by a process of splitting has 

 been advocated by several observers, Payne ('09) and Wilson 

 ('11) among them. These account for slight or gradual changes 

 but wide variations are accounted for by Wilson by a new 

 segregation of the nuclear material causing a change in number 

 and size relations of the chromosomes, but not in their essential 

 quality. Another method whereby a change might take place 

 is by an abnormality occurring in mitosis. Wilson ('09a) has 

 described an unequal distribution of the chromosomes to the 

 daughter cells in Metapodius. An arrest of cell division after a 

 division of the chromosomes has taken place was found by 

 Boveri ('05) in sea-urchin eggs. 



My material resembles McClung's ('05) in that the change 

 in number is accounted for by the fusion of chromosomes, these 

 giving rise to a multiple (V). However, the composition and 

 behavior of this multiple differs from the one described by him 

 in so far as its relation to the sex chromosome is concerned. 



These multiple or V-chromosomes resemble very much more 

 those being described by Robertson ('15) in Chorthippus (Steno) 

 bothrus). Robertson has found that Chorthippus {Stenobothrus- 

 curtipennis has seventeen chromosomes and of these, six are V's 

 (three pairs of V's). Counting each limb of the V as a chromo- 



