THE DIPLOID CHROMOSOME COMPLEXES OF THE PIG 193 



the nuclei of the other type, but the increase in number is 

 associated with a corresponding diminution in size." 



Meves ('11) found a graded series of chromosomes in the sala- 

 mander He did not believe that his results showed that pair- 

 ing exists, but it appears to me that the pairing in his material 

 is as marked as can be expected, considering the possibilities of 

 error through foreshortening and in drawing. This becomes 

 especially evident when the exceedingly long chromosomes of 

 the salamander are recalled. 



Robertson ('15) made use of a constant length relation be- 

 tween certain chromosomes to determine the amount of de- 

 ficiency of chromosomes which had lost a portion of their 

 length, and for the relation of the chromosomes of one type of 

 cells to that of another ('16). The relation of chromosomes in 

 the Orthoptera is evidently as constant as in the case of the two 

 forms I have studied. In a very few measurements of the chro- 

 mosomes of grasshoppers that I have made, the relationship 

 between pairs is very similar. 



I feel certain that many valuable results will be obtained 

 through the measuring of chromosomes and the study of their 

 relation to each other and to the chromosomes of closely related 

 groups. Other applications of these methods have been pointed 

 out in my paper on Oenothera scintillans ('18). In a prelim- 

 inary survey of the difference in length between the various 

 chromosome pairs of several plants and animals, I have "found 

 this relation (between pairs) to be practically constant in any 

 one group and, furthermore, in the few examples thus far exam- 

 ined, it does not vary greatly between widely separated groups. 

 What this means is, of course, impossible to imagine or predict 

 at present. It is exceedingly suggestive, however, of a physical 

 or physiological phenomena which future discoveries may show 

 to be of fundamental importance. 



Chromosomes in development 



At the beginning of this paper it was pointed out that an in- 

 vestigation of somatic chromosomes was really a study of the 

 ''behavior of chromosomes in development." We have not, I 



JOURNAL OF MORPHOLOGY, VOL. 30, NO. 1 



