180 ROBERT T. HANCE 



The conditions in the pig. With the increase in the number 

 of the chromosomes the difficulties of analysis are increased. 

 It is consequently necessary to know how far we may trust the 

 accuracy of the present work before it is possible to draw con- 

 clusions from the results. If the majority of the results obtained 

 in the present study can be shown to be safely comparable to 

 those obtained on O. scintillans, it will be justifiable to assume 

 that the conclusions reached for the earlier and more favorable 

 form will be applicable to the pig. 



A very interesting relation exists as regards the degree of 

 fragmentation in the two forms. Considering only the cells in 

 which the highest number of chromosomes is found in both the 

 Oenothera (21 chromosomes) and the pig (57 chromosomes) in 

 comparison to the type or fundamental numbers (15 and 40 re- 

 spectively), it becomes evident that the evening primrose has 

 suffered a fragmentation of 40 per cent of its chromosomes and 

 the pig of 42.5 per cent. While future work may show that this 

 percentage of fragmentation may mean nothing and is merely a 

 coincidence, for the present it is suggestive. 



To review briefly the results obtained in the study of the 

 chromosomes of the pig: 



1. The spermatogonial number is 40. 



2. The somatic nuniber as determined in the present study 

 ranges from 40 to 58. 



3. The 'extra' chromosomes divide as do the type chromo- 

 somes. 



4. A difference averaging 12 per cent has been found to exist 

 between spermatogonial pairs. If the relationships of the length 

 of the pairs on either end of the series be omitted the average 

 per cent is but five. 



5. The total length of the chromosomes of any somatic cell, 

 regardless of the number of chromosomes or of the tissues of 

 which it is a part, falls within the length limits found for the 

 spermatogonial chromosomes. 



6. The ' extra' chromosomes, for reasons set forth above, must 

 be fragments of the normal chromosomes. 



7. The fragments are very nearly of even length. 



