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THE PREDETERMINATION OF SEX IN 

 PHYLLOXERANS AND APHIDS 



T. H. MORGAN 



Department of Zoology, Columbia University 



FIVE TEXT FIGURES AND TWO PLATES 



CONTENTS 



Introduction 285 



The stem-mother's eggs 287 



The polar spindle of the male egg of Phylloxera fallax 289 



The chromosome cycle of Phylloxera fallax 290 



The chromosome cycle of Phylloxera caryaecaulis 291 



Sex ratios in Phylloxera fallax 295 



The spermatogenesis of the bearberry aphid ■ 297 



A tetraploid cyst in the bearberry aphid 301 



The omission of synapsis in the parthenogenetic eggs of phyloxerans and 



aphids 304 



Historical retrospect 309 



The life histories of certain aphids in relation to predetermination of sex. . 313 



Bibliography 316 



INTRODUCTION 



Two of the critical stages in the hfe of the phylloxerans of 

 the hickories have already been shown to be intimately connected 

 with changes in the cytological relations of the chromosomes. 

 One of these stages involves the formation of but a single class 

 of spermatozoa, that corresponds to the female-producing class 

 of other insects. This fact explains why the fertilized egg gives 

 rise to females only. The second critical stage involves the 

 elimination of chromosomes from the small eggs that are to be- 

 come males. This fact explains how the male comes to have 

 fewer chromosomes than the female, and brings him into line 

 with other Hemiptera, in which a similar relation holds. 



There is a third stage that might also be looked upon as a 

 critical stage ; namely, the stage at which the polar body is given 

 off from the egg of the stem-mother; because in P. caryaecaulis 

 after that event all of the offspring from one stem-mother are 



285 



