470 H. L. WIEMAN 



found by him, forty-seven, is about double that found by all 

 recent observers, for this prompts the suggestion that in this case 

 a doubling of chromosomes took place in early development. 

 However, for the present this case must stand as an anomaly, and 

 in view of the conclusions of all other workers in this field can not 

 be accepted as representing a typical condition. 



The differences in the form and size of the chromosomes, as 

 shown in the drawings, at first suggested a correlation between 

 these characters and the tissues in which they were observed. 

 Evidence for such an idea can be found in many cells, but is very 

 much weakened by the fact that these distinguishing features are 

 not constant, and the chromosomes of any tissue may appear 

 differently under different conditions. 



Figures 8 and 9 show prophases containing thirty-eight chromo- 

 somes, a number considerably above the average, thirty-four. 

 Figures 7 and 8 are both from the epithelium of the nasal pit, the 

 former showing thirty-four large chromosomes and the latter 

 thirty-eight, many of which are much smaller. In figure 9 a 

 number of the chromosomes are small in size. The same thing is 

 true of a few other cases where I have observed a relatively large 

 number of chromosomes in the somatic mitoses. These facts 

 suggest that the small chromosomes may be derived by a break- 

 ing up or 'diminution' of the larger ones. Likewise the differ- 

 ence between the somatic number and the spermatogonial num- 

 ber (as reported by Duesberg, Guyer and others) may have a 

 similar explanation; but in view of the scanty and questionable 

 character of the evidence, such an explanation can be offered only 

 in a very tentative way. In order to throw more light upon this 

 point, which is a highly important one in reaching any final con- 

 clusions in assigning a proper value to the chromosomes in the 

 organization of the cell, a comparative study of mitoses in embryos 

 of the same and different ages, together with an examination 

 of the maturation spindles, is necessary. I have made some head- 

 way in securing material for this purpose, which will serve as the 

 basis of a future study. 



