ABNORMAL MITOSES IN SPERM ATOGENESIS. 195 



which are produced by the normal portions of the testis. It is 

 interesting to note that Bridges ('21) has recertly reported a 

 case of triploidy in Drosophila which exactly fulfills these expec- 

 tations. The egg rather than the sperm, as could be determined 

 from genetic evidence, happens, however, to have been the gamete 

 affected, but the arrangement of the ovary is such that th; dif- 

 ference in sex dees not affect the applicability of the argument. 

 The facts which I have been able to make out in Euschistns prove 

 ( so far as they go ) that the presence of the chromosomes in the 

 tetraploid number, following some irregularity of unknown origin, 

 in no way affects the normal progress of spermatogenesis 1 (and 

 presumably of oogenesis as well). This is, I believe, the first 

 cytological evidence that abnormal germ cells, once established, 

 may thereafter proceed in an entirely normal manner probably 

 with the ultimate production of functional sperms (or eggs). 



These facts have a very interesting bearing on the origin of 

 triploid and tetraploid individuals, a matter in regard to which 

 opinion is at present in a very unsettled state. It has been held 

 by Gates ('09), with the subsequent assent of Strasburger, that 

 the doubling of the chromosome number (tetraploid individuals) 

 might arise " as the result of a suspended mitosis in the fertilized 

 egg or in an early division of the young embryo." Stomps ( '12), 

 on the other hand, has suggested that tetraploid individuals may 

 result from the union of two diploid gametes, triploid individuals 

 being obviously formed on this hypothesis by the union of a 

 haploid with a diploid gamete. 2 Further, the nature of the 

 chromosome group in a diploid gamete is again open to a dif- 

 ference of opinion, since it is evident that the diploid number may 

 have arisen from a normal (diploid) atixocyte through failure of 



1 Provided of course that other disturbing elements such as multiple cen- 

 trioles are absent. 



2 The possibilities of polyspermy have also been considered by Gates par- 

 ticularly in cases of triploidy, but our knowledge of this condition in animals 

 lends no support to the belief that it is ever a factor in the production of 

 triploid or tetraploid individuals. Further, both these authors were interested 

 almost exclusively in plants (in which (CEnothera, for example") triploid and 

 tetraploid individuals have actually arisen under observation), in which further 

 special possibilities (apogamy, for example) have to be considered that are 

 not met with in animals. These matters need not be considered further in 

 this paper. 



