CHKOMOSOME NUMBER AND PAIRS IN AMBYSTOMA 183 



form a series (fig. 31) like that (figs. 27 to 30) made by a similar 

 arrangement of the chromosomes of normal cells (figures 1 and 

 3). The length relationships of these chromosomes as shown 

 graphically in figure 37 are practically identical with those of 

 normal cells (figs. 33 to 36). Unfortunately, the cell walls are 

 not visible. 5) Both of the homologues of chromosome pairs, 

 as determined by measurements and indicated in figure 24 by a 

 duplicate series of numbers, in some cases are found in the 

 same separated part of the cell and in other cases one homologue 

 is found in part a and the other in part b. 



The third case is a compact metaphase in the epitheUum of 

 the lung (figs. 26 A and B) and is similar to the second case. 

 These two groups are somewhat more separated than those of 

 figure 24. Figure 26 B represents the chromosome number and 

 characteristics and figure 26 A shows the relative positions of 

 the two groups omitting some of the chromosomes in n. 



That these two groups of chromosomes are parts of the same 

 cell which have become separated is made highly probable by 

 the following facts: 1) As in the second case (fig. 24), the two 

 groups are near together, one containing eight and the other 

 twenty chromosomes — a total of twenty-eight. 2) The chromo- 

 somes are in the same stage of mitosis, the chromatids of those 

 of h, however, being separated a httle more than those of the 

 twenty chromosomes in a which may be due to a less crowded 

 condition. 3) The two groups are practically of the same 

 diameter and of the same shape. An outline of a on transparent 

 paper can be perfectly fitted to h. 4) These chromosomes also 

 form a linear series of lengths (fig. 32) similar to those of normal 

 cells. 5) Group a is not a complete cell because the cytoplasm 

 can be seen only below the chromosomes, while above the 

 chromosomes are bare. The boundaries of the cytoplasm of h 

 cannot be seen. 6) The homologues of the chromosome pairs 

 are numbered and distributed in the two groups like those of 

 figure 24. 



The fourth case is the peritoneum of another individual. It 

 evidently is a cell which has been divided into two parts like 

 those of cases 2 and 3. Figure 25 A is a camera-lucida drawing 



