grro kansas university science bulletin. 



trover sy over the chromosomes of Anasa. Foot and Strobell 

 publish photographs that seem to show that the accessory 

 chromosome divides in the second spermatocyte division. This 

 is their interpretation of the behavior of this element, and 

 they illustrate it by photography. Not a picture which they 

 publish would indicate that there is ever a case where the ac- 

 cessory chromosome positively fails to divide at this time, 

 and yet literally thousands of unqu^tionable cases of this 

 occur in every good preparation. See the group of cells 

 shown in figure 15, plate LXXI. By selecting a series of early 

 anaphases, and a very few obscure and distorted individual 

 cells, they are able to secure pictures which appear to bear 

 out their contention. In speaking thus of the methods of 

 Misses Foot and Strobell, I wish it clearly to be understood 

 that I am not reflecting upon their motives. It is my desire 

 only to show that photographs are interpretations of observed 

 phenomena and have no claim to infallibility. Again, as in 

 the case of the smear method, I would state that I speak as a 

 friend of the method and not as one who deprecates it. I 

 believe that scientific papers, particularly cytological, should, 

 whenever possible, be illustrated by photographs, and in my 

 own publications I have followed this plan so far as the 

 circumstances would permit. 



2. What is the number of spermatogonial chromosomes and 

 ^ of oogonial chromosomes ? 

 Confessedly, the accurate estimation of the numbers of chro- 

 mosomes in these generations of cells is a difficult matter, and 

 if it were the only means of determining the chromosomal 

 differences of the sexes there might be occasion for doubt with 

 regard to theories founded upon such enumerations alone. 

 Fortunately, it is only one of several criteria of sexual differ- 

 entiation in the germ cells, and so is not of commanding 

 importance. Accurate counts of the chromosomes, however, 

 are entirely possible with care, and concordant results are ob- 

 tainable by independent observers. In the case of Anasa this 

 is quite possible, and both Miss Pinney and myself have found 

 the number twenty-one uniformly present in the sperma- 

 togonia. Not a single instance of twenty-two chromosomes 

 was found in any spermatogonium, and we must therefore con- 

 clude with Wilson that thirty-one is the normal spermatogonial 



