214 



MONTGOMERY A STUDY OP THE CHROMOSOMES 



It may appear strange that the chromosomes of the spermaticls are classed as semi- 

 valent since they are generally considered univalent ; as I have explained in an earlier 

 portion of this paper, however, they must be regarded as semivalent on account of tin- 

 absence of a rest stage between the maturation mitoses, though they are virtually univa- 

 lent on account of their increase in mass during the growth period. Protenor lrlfr<nj> i 

 differs from the three other species in showing a bivalent chromosome in the spermatogo- 

 nium, which chromosome is consequently bivalent in the first spermatocyte even though 

 it unites with no other during the synapsis stage. All four species have in common the 

 phenomenon that the odd chromosome does not conjugate with any other during the syn- 

 apsis stage, but remains separate. In Alydus eurinus, Harmostes reflexulm, and Protenor 

 belfragei this odd chromosome does not divide in the second maturation mitosis, but passes 

 undivided into one of the two spermatids. In (Edancala dorsalis I was unable to deter- 

 mine its behavior in this mitosis, though I have no reason to suppose that here it behaves 

 differently from the other species. This unequal distribution of the odd chromosome in 

 the second maturation mitosis is evidently in some way dependent upon its not having 

 united with a fellow-chromosome during the preceding synapsis stage. What concerns us 

 particularly at present is the fact that in these species with an uneven normal number of 

 chromosomes, unlike those with an even number, one chromosome (the odd one) is not 

 divided in the second maturation mitosis, but passes undivided into one of the daughter 

 cells (spermatids); half of the spermatids then have six chromosomes and half have only 

 five. 



Bearing this point in mind, let us see how the uneven chromosomal number may be 

 perpetuated from individual to individual. This may be occasioned by one of two possi- 

 bilities. (1) The paternal germ cells having eleven chromosomes in the spermatogonia 

 and either five or six in the spermatids, there is the probability that the maternal germ 

 cells (ova) may have a corresponding number of chromosomes. If a spermatozoon with 



