vi FOREWORD 



Genetics in 1932 was mainly occupied in disproving Dr. Darlington's 

 conclusions. However, most of these objections have been quietly 

 withdrawn in the four succeeding years. The most important 

 correction to the views expressed in the first edition has been made 

 by Dr. Darlington himself. It is the discovery that in the males of 

 Drosophila, and doubtless of other Diptera, where there is no 

 genetical crossing-over, the meiotic autosomal bivalents are held 

 together not by chiasmata, but by attraction of a special character. 



This book is indispensable not only because of the discoveries it 

 describes, but almost equally on account of the coveries, to borrow 

 a word from Samuel Butler. A fundamental covery is that the 

 expressions " reductional division " and " equational division," 

 those bogies of our schooldays, are meaningless. For a given section 

 of a chromosome either meiotic division may be equational or 

 reductional. A teacher of biology may, for the sake of simplicity, 

 neglect some of the more recent discoveries in cytology. He 

 cannot neglect such a covery as this. 



It is perfectly possible that " Recent Advances in Cytology " 

 marks a turning point in the history of biology. For some centuries 

 the deductive method in the biological sciences has been very 

 properly suspect. But first in genetics, and now in cytology, we 

 have returned to it. General principles have been discovered of 

 such wide validity that we can predict from them with considerable 

 confidence, and on the rare occasions when the prediction is falsified, 

 we are inclined to look for undetected causal agencies rather than to 

 recast our first principles. This attitude has long been normal in 

 chemistry and physics. Its introduction into biology, however 

 unwelcome it may be to conservative biologists, is a sign of the 

 growing unity of science. 



J. B. S. HALDANE. 



