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, '14, '16 a, b; Hance, '17; 

 Holt, '17; \\Tiiting, '17) indicate these chromosomes to be paired. 

 Observations of pairs in a large number of animals and plants 

 have been extensively reviewed by Metz ('16, 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 ('11). 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 Delia Valle ('09, p. 109). He measured 

 both spermatogonia! and somatic chromosomes of various tissues 

 in Salamandra maculosa. Delia 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 '18 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- 



