vi PREFACE 



during the period, and the experience of each year has led 

 to modifications in the years that followed. But the general 

 plan has remained the same, and the writer believes that 

 it has proved to be of a kind to attract the interest of stu- 

 dents not previously familiar with the subject, and that 

 therefore a book of the kind might prove to be of value to 

 students in other laboratories. 



It is almost inevitable that a book of this kind should 

 reflect the special interests and prepossessions of the writer. 

 Cytology lies at the base of every biological phenomenon, 

 and at least to one engaged in biological research some 

 aspects of the subject must appear more interesting and 

 important than others. To attempt complete impartiality, 

 and to discuss every kind of theoretical application of cyto- 

 logical facts with equal thoroughness, would be an impos- 

 sible task even in a much larger book, and would probably 

 lead to a very uninspiring presentation of the subject. 

 While trying, therefore, to point out the importance of 

 various aspects of cytological study, it is possible that the 

 book errs in devoting too much space to those sides of the 

 subject in which the writer is chiefly interested, especially 

 the cytological basis of hereditary transmission and of sex- 

 determination. But even if it may appear to some that the 

 treatment is lop-sided in this respect, one good excuse may 

 be urged which is not of a personal nature. By far the 

 greater part of cytological research during the past fifteen 

 years has been devoted, directly or indirectly, to these 

 questions, and though in years to come it may seem, quite 

 rightly, that cytologists have been far too exclusively occu- 

 pied with one group of problems, it is hardly possible at 

 the present time not to emphasise them, even at the expense 

 of others that are in fact of no less importance. If the treat- 

 ment is lop-sided, it may fairly be said that it reflects the 



