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. Della Valle’s measurements. Della 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, 
