9 8 



THE DETERMINATION OF SEX 



picture shows us a polar view of an equatorial plate of the 

 second division. The ordinary chromosomes form a circle; 

 in the center we see the accessory chromosome, which in this 

 genus is not simple but quadripartite. Fig. 50 is a drawing 

 from Syromastes, offering a polar view of the first division. 

 Wilson discovered in this genus a double accessory chromo- 

 some which does not lie in the center of the equatorial plate 

 but outside the circle of the remaining chromosomes. Quite 

 similar is the last photograph of our series, Fig. 51, which is 



FIG. 49. FIG. 50. FIG. 51. 



FIG. 49. Galgulus oculatus. Polar view of A the equatorial plate of the second 

 spermatocyte division. The accessory chromosome is quadripartite, and lies in the 

 center. 



FIG. 50. Syromastes marginatus. First spermatocyte division. The accessory 

 chromosome is bipartite and lies peripherally. 



FIG. 51. Metapodius terminalis. First spermatocyte division. The accessory 

 chromosome lies peripherally, and alongside it is a Y-chromosome. 



taken from Metapodius. In this case the accessory chromo- 

 some is simple and lies outside, while near it occurs a Y- 

 chromosome which is very similar in appearance to the acces- 

 sory, but differs from it in its further development. In the 

 center of the equatorial plate lies a minute chromosome, the 

 meaning and history of which is not yet completely cleared up. 

 The photographs from which these drawings were made are 

 very beautiful and render the relations perfectly clear. 



Miss Stevens was a gifted and eager investigator, whose 

 early death brings a heavy loss. In the year 1911, she pub- 



