THE ACCESSORY CHROMOSOME. "J I 



From this it will be apparent enough why there is an undi- 

 vided chromatin element in one spermatocyte mitosis. It is but 

 a single chromatid and so cannot be separated into halves. If, 

 therefore, Paulmier bases his theory upon this phenomenon 

 (as it appears he does) it would seem that he has a very insuffi- 

 cient foundation for it. True it is that he considers the element 

 a tetrad and so would be more justified in his conception, but the 

 evidence he brings forward in the proof of this is not convincing. 

 Montgomery clearly recognizes its unit character in other mem- 

 bers of the Hemiptera, Sutton traces it through the spermato- 

 gonia of the Orthoptera as a single chromosome, and my own 

 observations are positive as to its valence. The weight of evi- 

 dence is therefore strongly against Paulmier on this point the 

 essential one in his theory. Moreover, I might point out that 

 the division of the elements has already been accomplished in 

 the prophase of the first spermatocyte and only their separation 

 remains for a succeeding metaphase. The active agents here 

 are the archoplasmic fibers, so that failure to act in unison with 

 the other cell structures would reflect upon their vigor rather 

 than upon that of the chromosomes. 



Again, the great regularity of the divisions by means of which 

 exactly one half of the spermatozoa are unprovided with the ele- 

 ment would seriously weaken any assumption of degeneration. 

 If the usual course of degenerating structures were followed, it 

 would demand great irregularity and uncertainty in the occur- 

 rence of the unequal division, whereby varying numbers of the 

 spermatozoa would be marked by the presence of the undivided 

 element. In none of the forms studied is there any suggestion 

 of an indeterminate and indefinite division, and in the absence of 

 this, Paulmier's theory loses its strongest support. 



It is also pertinent to ask whether the dropping of specific 

 characters would take place by the elimination of an entire chro- 

 mosome, if so whether this would occur in the germ cells, and, if 

 in the germ cells, why in the last generation ? 



In view of all the objections advanced, I believe it would be 

 impossible for Paulmier's hypothesis to maintain its ground with- 

 out the support of numerous others equally difficult to base 

 upon observed facts. It will be necessary on this account to 



