THE DIPLOID CHROMOSOME COMPLEXES OF THE PIG 161 



Methods of measvjring 



The chromosomes were enlarged with a pantograph six diame- 

 ters over the original magnification (which was 3400 X). This 

 not only made easier to measure the chromosomes but gave 

 somewhat more accurate results. Many of the chromosomes are 

 practically straight, so that a rule could be used in measuring. 

 The automatic map measure was employed in obtaining the 

 length of the curved chromosomes. The advantages of this in- 

 strument have been described (Hance, '18). It has the dis- 

 advantage that millimeters must be estimated. This, I believe, 

 I have been able to do with an error of at the most not more 

 than one or two millimeters. With the large magnification of 

 20,400 X these results appear to me to be sufficiently accurate. 



Mechanical aids 



The automatic tally register has been found a great conveni- 

 ence for counting the chromosomes. It enables the investiga- 

 tor to go from the drawing to the microscope without the neces- 

 sity of remembering the number that has already been counted. 

 The chromosomes are, of course, checked as counted. Before 

 this device was tried drawings would frequently have to be 

 counted several times to be certain that no error had been made. 



An adding machine has been of the greatest" assistance in this 

 work as has also a 'Calculex,' or circular slide rule, which was 

 used for determining percentages. 



A large number of drawings of mitotic figures are presented 

 with this paper, partly to counteract the general impression, 

 gained from published mammalian studies, that clear figures are 

 difficult to find, but largely to give a better idea of the appear- 

 ance and relationship of the chromosomes of the various cells. 



ACKNOWLEDGMENTS 



For material I am exceedingly grateful for tjie courtesies ex- 

 tended me by the Pitmann-Moore Biological Laboratories of In- 

 dianapolis, by Mr. Clarence Keen of Kingan and Company, packers, 

 of Indianapolis and by Dr. Reed of the Mulford Biological Farm 



JOURNAL OF MOHPHOLOGY, VOL. 30, NO. 1 



