212 CHARLES L. PARMENTER 



mental and personal error of about 0.6 mm. at his magnification. 

 This, of com'se, is negligible in comparison with the large errors 

 arising from foreshortening in numerous chromosomes. 



Concerning the favorableness of the spermatogonial chromo- 

 somes for measurement, Meves says (p. 274) that bj^ no means 

 do all of the chromosomes lie in the equatorial plane; without 

 exception the bend lies in the plane while the ends lie outside; 

 in the drawings such chromosomes seem shortened and therefore 

 the measurements upon these chromosomxcs would give only an 

 approximate value. Judging from these statements and from 

 the magnitude of error due to the slight foreshortenings in my 

 material, his measurements very likelj'- contain errors which 

 amount to as much as 4 or 5 mm. 



For measurements of somatic chromosomes he chose (p. 280) 

 polar views of the transformation stages between the prophase 

 and metaphase stages in the epithelium of the gill plates (figs. 16 

 to 18) and extraordinarily well-flattened polar views of pro- 

 phases (figs. 11 to 13) and metaphases (figs. 14 to 15) in the 

 peritoneum. In the three prophases of the peritoneum the chro- 

 mosomes lay nearly or entirely parallel with the upper surface 

 of the cell. According to this description, it is evident that these 

 three prophases are the most favorable cells, and even in these 

 the chromosomes are not entirely free from foreshortening. The 

 chromosomes of the other cells probably were more foreshortened. 

 Therefore, judging from results in Amby stoma, his measurements 

 contain errors due to foreshortening which probably vary from 2 

 to 5 mm. ' 



The amount of the errors which are due to the twisting of the 

 chromatids of these chromosomes is uncertain. Such twisting is 

 evidently present, as indicated by the irregular contour of his 

 chromosome drawings which are similar to those of my own. 

 The errors due to this twisting may largely neutralize each other 

 as explained above (p. 189). He mentions also the possibility of 

 different rates of contraction of the chromosomes, especially in 

 the earlier stages. Having before us the conditions under which 

 Meves made his measurements, we are in a position to judge 

 their value more or less correctly. 



