34 ORILLA STOTLER WERNER. 



metaphase (Fig. 4); Fig. 47, and 48 are from late prophases 

 (Figs. 1,2). 



The morphological groups and the size relations within the 

 groups are very evident in this comparative series. The distinc- 

 tion in size, etc., between the group ot twelve (thirteen in the 

 female) large chromosomes (38-33) and the group of 18 of inter- 

 mediate size (32-24) is clearly marked in Plates 7 and 8. This is 

 especially true in Figs. 37, 38, 40, 43, 44 and 45. It may also be 

 plainly seen that the intermediate-sized and the globe-shaped 

 chromosomes each form a finely graduated series. Because of 

 this finely graduated condition and because there are so many of 

 them there may have been some inaccuracy in the pairing and, in 

 the case of the globe-shaped series, possibly in the count also, for 

 these, the smallest chromosomes, frequently overlie one another. 

 But it is certain that there is no inaccuracy in the count in the 

 cases of the members of the larger and of the intermediate-sized 

 groups. There is clearly 12 plus 18, or 30, of these bodies in the 

 cells of the male and 13 plus 18, or 31, in the cells of the female. 

 Neither can there be any doubt as to the presence of at least 

 one unpaired chromosome among those from the female, for it is 

 larger than and morphologically different from the other chromo- 

 somes. In the case of the chromosomes which have been arbi- 

 trarily numbered 38w and 38Z it might be said one is dealing with 

 gonial mates, since they are similar in length and contain ap- 

 proximately the same amount of chromatin. These facts, how- 

 ever, considered alone, are not sufficient proof that they should be 

 considered homologous rather than that they might be, as I shall 

 attempt to prove later, two additional odd chromosomes which 

 are concerned with the sex-mechanism. The important point in 

 this paper is the fact, previously indicated, that a study of the 

 cells of the male reveals an even number of the larger chromo- 

 somes while a study of the cells of the female shows an odd num- 

 ber and one more than in the cells of the male. 



The morphological difference of the last group of chromosomes 

 (globe-shaped) from the two preceding groups is not a condition 

 peculiar to the duck. Painter shows the same condition in the 

 lizard (Figs. 35, 36). As previously stated the twenty- two 

 smallest chromosomes are so small and so closely graduated as to 



