ACCESSORY CHROMOSOME IN ANASA TRISTIS. 125 



his results and would not presume to do so were it not possible 

 to corroborate our observations with photomicrographs in which 

 22 chromosomes can be counted without any question. We 

 realize in common with all cytologists the difficulty of getting a 

 correct count of so large a number of small bodies crowded into 

 a contracted space. If 2 or more chromosomes are in such close 

 contact that their line of separation is obscured a correct count 

 is impossible. It is certainly possible to find cells in which only 

 2 1 chromosomes can be differentiated and still easier to find cells 

 in which only 20 or 19 are defined. It is much more difficult to 

 find each chromosome so distinctly isolated that all can be demon- 

 strated in one photograph. 



Wilson ('c>5-'o6) corroborates his original count of 21 sperma- 

 togonial chromosomes and illustrates this point in four sketches. 

 Montgomery ('06) in his last paper withdraws his earlier estimate 

 of the number and supports Wilson's results, figuring 21 chromo- 

 somes in his sketch No. 151. 



In view of this weight of authority we do not feel inclined to 

 be in the least dogmatic in our estimate of the count of the 

 chromosomes, but our preparations certainly justify us in main- 

 taining that it is possible to demonstrate 22 spermatogonial 

 chromosomes in Anasa tristis, as we shall show later in photo- 

 micrographs of the preparations themselves. 

 December I, 1906. 



1 " Since this paper was sent to press I have determined beyond the possibility of 

 doubt, I think, that the number of spermatogonial chromosomes in Aiiasa tristis is 21 

 not 22 as given by both Paulmier and Montgomery. This result is based on a study 

 of a large number of preparations and careful camera drawings of more than 20 per- 

 fectly clear metaphase figures have been made. All without exception show 2 1 chromo- 

 somes, and I have sought in vain for even a single cell that shows 22." 



