Vol. XXXI. August, i pi 6. No. 2 



BIOLOGICAL BULLETIN 



EIGHTY-SEVEN GENERATIONS IN A PARTHENO- 

 GENETIC PURE LINE OF APHIS AVEN/E FAB. 



H. E. EWING. 



The chief features of my work with Aphis avence Fab. are here 

 summarized : 



1. The pure line theory, as originally applied to self-fertilized 

 plants or asexually reproducing plants and animals, was tested 

 in eighty-seven generations of a parthenogenetic insect. 



2. Selections were made for forty-four consecutive generations 

 in an attempt to modify a character that is known to be easily 

 modified by selection in higher animals that reproduce sexually. 



3. Variations, both continuous and abrupt, were studied in 

 regard to their transmissibility. 



4. The occurrence of paedogenesis is here recorded. 



5. The effect of continued parthenogenetic reproduction on 

 the virility and metabolism of a strain has been determined. 



6. The effects of temperature on growth, size, reproduction, 

 and dimorphism are here noted. 



INTRODUCTORY CONSIDERATIONS. 



About three years ago when the writer began his studies in 

 pure lines, it appeared that the time was quite opportune for 

 some one to carry on breeding experiments with some partheno- 

 genetic insect. Up to that time no one had tested the pure line 

 theory of inheritance in any of the higher arthropods. After 

 attempting breeding work, first with our common cabbage aphis, 

 Aphis brassicae Linn., and later with the black cherry aphis, 

 Myzus cerasi Fab., I finally started the experiments with Aphis 

 avencs Fab. which are here reported. A very few of the results 



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