CHROMOSOME NUMBER AND PAIRS IN AMBYSTOMA 213 



As Meves states (p. 276), the differences in length between the 

 spermatogonia! chromosomes are too small, and the possible 

 errors too great to affirm that these chromosomes are present in 

 pairs of equal length. On the other hand, it should be added 

 that these conditions offer no evidence against this claim. 

 Furthermore, he shows a practically constant difference in 

 length of 6 half-millimeters between chromosomes 8 and 9 in 

 his table of measurements. An examination of these figures 

 shows unmistakable evidence that there is foreshortening in chro- 

 mosome 9 in three of these cells, and a probability that chromo- 

 some 8 is much less, if any, foreshortened than chromosome 9. 

 There results, therefore, in all of these cells a relatively uniform 

 distribution of the chromosomes into two constant groups, a 

 point which supports the claim that the relative lengths of these 

 chromosomes remain constant. 



Concerning the somatic measurements, Meves concludes (p. 

 282) ''Die Fragen, ob bei gewohnlichen Gewebszellen des Sala- 

 mandra Chromosomenpaaren unterschieden werden konnen, ist 

 bereits von C. Rabl ('06, S. 72) verneint worden, ich muss mich 

 ihm auf Grund der mitgeteilten Zahlen anschliessen" and '"Die 

 erhebliche Langendifferenz zwischen chromosomen VIII und 

 IX, welche wir bei den Spermatogonien festgestellt haben, 

 besteht bei den gezeichneten somatische Zellen nur in der Halfte 

 der Falle." This means, of course, that he believes that the 

 chromosomes are not distributed into two constant groups in 

 each cell and that therefore the evidence of the constant organi- 

 zation of the chromatin is lacking in this respect. 



As already stated, the possibilities of error are so great that 

 nothing is conclusively affirmed or denied by his measurements. 

 However, an examination of the drawings of the chromosomes in 

 his figures indicates certain probabilities. 



1. In three of the four cells (his figs. 15 to 17) in which the 

 marked difference between chromosome 8 and 9 is not present^ 

 chromosome 9 is conspicuously foreshortened, and is in reality 

 longer than his measurements indicate. Furthermore, chromo- 

 some 8 in these cells may or may not be foreshortened, at any 

 rate it is probablj^ much less foreshortened than chromosome 9. 



