THE DETERMINATION OF SEX 89 



to demonstrate that the accessory chromosome does not 

 determine the formation of males but of females. The ac- 

 cessory chromosome was first seen by a German, Henking, 

 and was afterward studied by the American, Montgomery. 

 McClung was the first to recognize its true nature and import- 

 ance, and to him belongs the honor of having first brought the 

 investigation of the determination of sex upon' the proper road. 



The formation of the sexual elements is fuU of meaning 

 and interest, but it cannot be made clear by words alone. 

 On account of the importance of the phenomenon I wish now 

 to show you certain pictures which are suited to clarify your 

 impressions. 



The sexual cells, like all cells, are little adapted in their 

 natural state to microscopic observation. Special methods 

 have been invented to overcome this difficulty. In most cases 

 thin sections are made of the organ or tissue which it is de- 

 sired to investigate. The sections are artificially colored. 

 We should have been able to learn little of the structure of 

 cells without this method. The pictures which I have to 

 present to you have been made from artificially colored prepa- 

 rations. The chromosomes which we wish specially to ob- 

 serve are colored almost black, while most of the rest of the 

 cell appears gray. Our pictures are all, except Fig. 44, draw- 

 ings for the most part from photographs. In the drawings 

 only the black parts have been put in, and in most of them 

 only the chromosomes are represented. When a sexual cell 

 begins to transform itself into a sexual element the nucleus 

 passes through a series of changes during which the chromo- 

 somes assume wonderfully irregular forms, which, however, 

 quickly change again. Our first picture* is a drawing by a 



* The picture mentioned was projected on the screen for the lecture, and is not 

 reproduced here. The conditions are similar to those represented in Fig. 52. 



