A COMPARATIVE STUDY OF THE CHROMOSOMES OF 

 SIX SPECIES OF NOTONECTAi 



ETHEL NICHOLSON BROWNE 



Zoological Laboratory, University of California 



ONE HUNDRED AND FIFTEEN FIGURES (SEVEN PLATES) 



CONTENTS 



I. Introduction 119 



II. Species of Notonecta 121 



III. Brief summary of the chromosomes of N. undulata, N. irrorata, and 



N. insulata 122 



IV. The chromosomes of N. glauca 123 



a. Observations 123 



b. Comparison with results of Pantel and Sin^ty 128 



V. The chromosomes of N. shooterii 129 



a. Observations 129 



b. Size relations of X and Y 131 



VI. The chromosomes of N. indica '. . 132 



a . Observations 132 



b. The X chromosome of N. indica 135 



VII. Comparison of the chromosomes in the six species 137 



a. Autosomes 137 



b. Sex chromosomes 140 



VIII. Correlation of somatic characters and chromosomes 141 



IX. Constancy of the chromosomes 144 



X. Summary 144 



XI. Literature cited 146 



I. INTRODUCTION 



A previous study of the chromosomes of three species of Noto- 

 necta (Browne '13) proved of such interest as to lead me to un- 

 dertake a more comprehensive study of the chromosomes of 

 this genus. It is with the view of making a comparative cyto- 

 logical examination of all the species of this genus that the pres- 

 ent paper is written dealing with three additional species. Ow- 

 ing to the fact that certain chromosomes are characteristic in 



^This work was done while holding the Sarah Berliner Research Fellowship. 



119 



