From the Biological Laboratory of Bryn Mawr College. 



A STUDY OF THE GERM CELLS OF APHIS ROSE 

 AND APHIS (ENOTHER.E.i 



BY 



N. M. STEVENS. 



Associate in Experimental Morphology, Bryn Mawr College, and Research Assistant, Carnegie Institution 



of Washington. 



With 4 Plates. 



ft 

 I. Material and Methods -^14 



II. Parthenogenetic Development 314 



1 . Female Line 314 



2. Male Line 316 



III. The Winter Eggs 318 



1. Early Development and Growth 318 



2. Maturation 320 



IV. Spermatogenesis 321 



V. General Discussion 323 



1. Mendel's Law. and the Individuality of the Chromosomes 323 



2. Maturation of Parthenogenetic Eggs 324 



3. Determination of Sex 326 



VI. Summary of Results 329 



This work was undertaken in connection with a series of experi- 

 ments on sex-determination in Aphids. On approaching the 

 subject, It was found that very Httle is known concerning the ovo- 

 genesis and spermatogenesis of these insects. Blochmann ('87) 

 showed that the parthenogenetic egg gives off one polar body, and 

 the winter egg two; but I find no account of the number of chro- 

 mosomes or the method of reduction in either egg, nor is there any 

 pubhshed work on the spermatogenesis of Aphids. The present 

 paper will be devoted mainly to the germ-cells, a few points in the 

 early stages of parthenogenetic development being considered 

 incidentally. 



'This paper was awarded the prize of one thousand dollars offered in 1904 by the "Association 

 for Maintaining the American Woman's Table at the Zoological Station at Naples, and for Pro- 

 moting Scientific Research among Women."" 



