INTRODUCTION 



I HOPE that this book will be of use to many bio- 

 logists who realize that chromosome -cytology has 

 made considerable progress in the last ten years, and 

 that the existing text-book apcounts of mitosis and 

 meiosis are hopelessly inaccurate, but who have no 

 time to read the larger works of Darlington and B^lar, 

 which must remain the standard sources of information 

 on the subject. 



Chromosome cytology is essentially a practical sub- 

 ject, which can only be thoroughly mastered by a 

 study of actual preparations under the microscope. 

 Unfortunately this study is usually regarded as too 

 difficult to be included in a degree course in biology. 

 It is surprising, however, how much can be seen, even 

 without using an oil-immersion objective, provided 

 that one chooses suitable material with large chromo- 

 somes. There is no doubt that for most purposes the 

 testes of Locusts and Grasshoppers (any species will 

 do) provide the best introductory material. They 

 should be fixed in Flemming's solution and stained 

 in one of the aniline dyes like Gentian Violet. In the 

 course of the past year I have made the ordinary 

 degree students in this department work through 

 material of this kind (sectioned at 25 // so as to 

 obtain whole nuclei). They were able to see all 

 the stages of mitosis and meiosis and even to work 

 out the average number of chiasmata per nucleus in 

 three different species. That it is possible for students 

 to do this in a course involving only one afternoon a 

 week should destroy the myth that cytology is a 

 fantastically difficult subject. 



In a book of this size it is necessarily not possible 



