CHROMOSOME NUMBER AND PAIRS IN AMBYSTOMA 
211 
equal lengths in the early spireme and metaphase stages. The 
general observations of many later authors, especially those 
studying Dipteran somatic cells (Metz, T4, T6 a, b; Iiance, T7; 
Holt, T7; Whiting, T7) indicate these chromosomes to be paired. 
Observations of pairs in a large number of animals and plants 
have been extensively reviewed by Metz (T6, p. 245). 
But no cases are recorded in which an attempt was made to 
determine accurately by measurement what relation the lengths 
of somatic chromosomes bore to one another until the work of 
Meves (’ll). As a result of the discussion centering around the 
observations of Montgomery (’01) and Sutton (’02), he was led 
to attempt measurements in an effort to obtain more definite 
data, as suggested by Della Valle (’09, p. 109). He measured 
both spermatogonial and somatic chromosomes of various tissues 
in Salamandra maculosa. Della Valle (’12) made further meas¬ 
urements upon the same form, and agrees with Meves that their 
results do not confirm the observations of Montgomery and 
Sutton. Hance (’17 and T8 a) interprets his measurements 
upon the somatic chromosomes of Oenothera scintillans and the 
pig as confirmatory. • 
1. Meves’ results. Since Meves has (p. 282) failed to confirm 
the results of other authors, it is desirable to reconsider his data 
in comparison with linear measurements upon cells of the same 
nature in the same kind of preparations and of the same tissues 
of another salamander, Ambystoma tigrinum, in an effort to form 
a judgment of the validity of’his conclusions. For this purpose 
it is necessary to recall what criteria are required (p. 191) 
definitely to affirm or to deny the existence of pairs and under 
what conditions these criteria were satisfied. 
The following conditions under which Meves’ measurements 
were made allow the introduction of such a varying amount of 
error that the conclusions drawn from his results are of question¬ 
able value. 
Instrumental and personal errors. Meves made his measure¬ 
ments evidently upon a single drawing, probably somewhat care¬ 
fully executed, which means, according to a series of tests in my 
own attempts to be accurate, that he has a minimum instru- 
