S p>er}}iatogenesis 473 



seem to undergo their reducing division when the odd chromosome is 

 dividing equationally, but this is only a further mark of the indi- 

 viduahty of the chromosomes, and does not furnish any evidence 

 against Montgomery's theory of synapsis. Medes ('05) finds a 

 similar condition in Scutigera forceps. 



Orthoptera 



Neither vom Rath ('91, '92) nor Wilcox ('95) noticed an odd 

 chromosome in Gryllotalpa or Caloptenus, although both mention 

 a nucleolus in the spermatocyte growth period which may be the 

 same structure. They both insist that there are two reducing 

 divisions; that is, two divisions that separate whole chromosomes 

 from each other. This is probably due to a confusion in the use 

 of the word chromosome. If we use the terminology suggested by 

 McClung ('00), univalent chromosome in the spermatogonium, 

 bivalent chromosome in the spermatocyte, and chromatid for each 

 unit of the tetrad, the discrepancies in the work of vom Rath and 

 Wilcox are cleared up. Vom Rath finds 12 spermatogonial chro- 

 mosomes. In the growth period, the spireme splits into six rods, 

 each of which forms a tetrad, or divides into four "chromosomes," 

 as he expresses it. As he calls each chromatid a chromosome, he 

 considers that he has two divisions which separate chromosomes 

 from chromosomes; and therefore must be reducing; while in 

 terms of the original spermatogonial chromosomes, one division 

 is reducing and one equational. Wilcox falls into the same diffi- 

 culty; he finds 12 spermatogonial chromosomes, and then the 

 spireme divides into 24 "chromosomes," which form 6 tetrads. 

 He had, in reality, 24 chromatids, and only one reducing divi- 

 sion. 



McClung ('00, '02a) has described the odd chromosome in the 

 Acrididae and Locustidae. He worked on a number of forms and 

 obtained uniform results. In the Orthoptera, this chromosome 

 can be traced back into the spermatogonial rest stages. It divides 

 only in the first spermatocyte division, giving dimorphism of the 

 spermatozoa. In 1901, McClung suggested the theory which has 

 since that time received substantial corroboration, that the dimor- 



