CHROMOSOME NUMBER AND PAIRS IN AMBYSTOMA 215 



and 13 showing late prophases in which there is usually much 

 foreshortening and considerable inequality of homologues, as 

 stated above. In five other cells (figs. 14 to 18) Meves' figures 

 show but one case of a difference of 3 mm. and only five cases 

 of a difference of as much as 2.5 mm. between homologues, as 

 they are indicated by his measurements. But the various 

 sources of error already mentioned make it uncertain as to what 

 the actual lengths are. 



To summarize the examination of the results of Meves' 

 measurements, it may be said, 1) that the chromosomes of the 

 spermatogonial cells fall into two groups, one containing chro- 

 mosomes 1 to 8, the other chromosomes 9 to 24. 2) In the 

 somatic cells, when corrections are made for evident fore- 

 shortenings, it is probable that in eleven of the twelve cells, and 

 possibly also in the twelfth, the same grouping is present. This 

 indicates a constancy of organization of the chromatin. 3) It 

 is impossible either to demonstrate conclusively or to deny that 

 these chromosomes are paired because, a) of the various sources 

 of error present and, b) the small differences in length in the 

 majority of cases between adjacent chromosomes. 



2. Delia Valle's measurements. Delia Valle ('12) measured 

 the lengths of chromosomes in the peritoneal cells of Salamandra 

 maculosa shown in his ('09) figures 1 to 3, 8 to 9, and 12. The 

 length of each chromosome was obtained by averaging two 

 measurements made with a curvimeter upon a single camera- 

 lucida drawing. He also attempts to determine the degree of 

 concordance between the measured lengths of each of these 

 chromosomes and the dimensions which would exist if the 

 lengths of these chromosomes were determined by the laws of 

 fluctuating variation. These latter figures he obtains by calcu- 

 lation from a table of figures compiled by Sheppard and pub- 

 lished by Galton ('07). He interprets his data as demonstrating, 

 1) that the chromosomes of Salamandra maculosa do not exist in 

 pairs; 2) that there is no constant grouping of chromosomes, 

 such as is evident in the measurements of Meves and myself, 

 and, 3) that the chromosomes are a series of variants subject 

 to the laws of fluctuating variation as shown by the comparison, 



