ABNORMAL MITOSES IN SPERMATOGENESIS. 197 



In plants, on the other hand, it occurs more commonly in 

 CEnothcra for example, where the repeated occurrence of unusual 

 chromosome complexes would perhaps indicate that some unstable 

 condition exists which would increase the probability of a coinci- 

 dent production of diploid gametes of both sexes. 



The viewpoint which I have here tried to develop may be 

 summarized in the following way. A normal, diploid zygote is 

 formed by the union of two haploid gametes. 1 After a number 

 of divisions the germ cells (one or more?) are segregated, and 

 these then multiply to form the primordial germ cells and sub- 

 sequently spermatogonia (or oogonia). An abnormal division 

 at some early stage resulting in a doubling of the chromosomes 

 might conceivably give rise to a gonad composed entirely of 

 tetraploid cells a condition never yet observed. A similar ab- 

 normal division in one of the primordial germ cells would result 

 in many cysts of tetraploid spermatogonia (or oogonia), as I 

 have found in the EiiscJiistiis case certainly a rare phenomenon 

 or it would have been long since reported. Proceeding still 

 further, a similar abnormal division at the time a cyst of sperma- 

 togonia (or oogonia) is begun, would give rise to a single cyst 

 of tetraploid cells (see the case reported by Morgan, '15), while 

 abnormal divisions at a subsequent time might give rise to one or 

 several tetraploid cells among many normal ones in the same 

 cyst. The tetraploid cells thus produced undergo normal synapsis 

 and reduction, but the chromosome number, being thus diminished 

 only by the usual one half, is diploid in the resulting gametes. 

 The union of such a diploid gamete with a normal (haploid) one 

 produces a triploid individual, while the union of two sucli dip- 

 loid gametes (due to a very rare coincidence ) produces a tetraploid 

 individual. 



In conclusion, it may be noted that the behavior of the chromo- 

 somes in the Eiiscliistus case adds further evidence to that already 

 accumulated tending to demonstrate the genetic continuity of the 

 chromosomes. In the same testis there are (normal) diploid 

 and (abnormal) tetraploid spermatogonia, each of which gives 



i It is conceivable that, as Gates suggests, the first (or other early) cleavage 

 might be suppressed, resulting in a tetraploid individual, but there is no 

 evidence among animals that this ever occurs, and the difficulties in the way 

 of such an explanation are great. 



