IHE DETERMINATION OF SEX 



97 



them contain a still distinct accessory chromosome, which in 

 the other half of the heads cannot be seen. This picture 

 affords unquestionable proof that there really are two kinds 

 of spermatozoa. The next pictm:e, Fig. 45, is from Alydus, 

 and demonstrates to us again the second division and the 

 wandering of the accessory chromosome. Next follows a 

 drawing of Pyxrochoris, Fig. 46, which represents the second 



^' 



Fig. 47. 



Fig. 46. — Pyrrochoris apterus. Division of the 

 second spermatocyte. 



Fig. 47. — Anasa tristis. 6 Two views of dividing 

 female nuclei (oogonia). 



Fig. 48. — Anasa tristis. 6 The second spermatocyte division. The accessory 

 chromosome is lodged at one pole and is lacking at the other. 



Fig. 48. 



division almost completed. Both cells are clearly recogniz- 

 able, but only one of them contains an accessory chromosome. 

 Next follows a drawing from Anasa, Fig. 47, which is shown 

 because it presents to us two views of the cell division. In 

 the upper ceU we have a side view of the spindle, and we notice 

 at once the so-caUed equatorial plate which is formed by the 

 collocation of aU the chromosomes in the equatorial plane. 

 The lower cell is a view of an equatorial plate seen from the 

 spindle pole. Next comes a picture from Anasa, Fig. 48, 

 which shows us the second division nearly completed. The 

 wandering of the accessory chromosome is very clear. We 

 pass now to the consideration of Galgulus, Fig. 49. The 



