464 H. L. WIEMAN 



OBSERVATIONS 



Mitoses are abundant in every tissue of the body except the 

 endoderm of the ahmentary canal, the epidermis and the germ 

 cells, most of which are in the resting condition. The germinative 

 layer of the central nervous system shows the greatest number of 

 division figures. The sex of course could not be determined. 



Prophases were found most favorable for study, and at this 

 stage counts could be made with relative ease and accuracy, 

 although in all cases the chromosomes lie at different levels. A 

 scattering of the chromosomes throughout the cell is characteristic 

 and sometimes a partial division with incomplete separation of the 

 halves occurs before the metaphase. 



In selecting cells for illustration, I have considered only cells 

 that are uncut by the knife and entirely included in the section. 

 However, conclusions are based on the study of a much larger 

 number, many of which might have been drawn. In many 

 instances it is impossible to determine the number exactly owing 

 to overlapping and crowding; but these are nevertheless useful 

 when interpreted according to other cells indisputably clear. 

 The number of the latter is not great, in spite of the large number 

 of dividing cells in the material; for but relatively few combine 

 the advantages of position in the section and sharp demarcation 

 of the chromosomes from one another. 



Figure 1 is from a liver cell. The chromosomes, thirty-four in 

 number, are in the form of rods, usually straight, but sometimes 

 curved, or bent into Vs. No attempt has been made to pick out 

 synaptic mates, but it can be readily seen that some of them fall 

 into series of pairs, according to size and form (1, 2, 3). 



Figure 2 represents a remarkably clear prophase in a cell from 

 the germinative layer of the brain in which the number of chromo- 

 somes is thirty-three. The chromosomes are somewhat thicker 

 than in the preceding cell. Figure 5 is also taken from the brain. 

 This cell is ruptured so that the chromosomes are spread out as 

 in a smear preparation, making the task of counting them a very 

 simple matter. The number is thirty-three or thirty-four, depend- 

 ing upon whether or not we exclude the body marked z, which is 



