SUMMARY OF RESULTS. 13 



^ 



SUMMARY OF RESULTS. 



1. Each species of aphids is characterized not only by a specific 

 number of chromosomes, but by peculiarities in their form and size, 

 and in some cases by a definite arrangement, as in the clover aphid, 

 the pale milkweed aphids, and the second oak aphid described (figs. 

 58, 59, 73, 74, 94). Where the number of chromosomes is the same 

 in two species, there is always some characteristic difference in form 

 or size corresponding to the external differences in the species. 



2. No evidence of hybridism has been observed where two or more 

 species occur on the same host. 



3. There is no evidence of any reduction in the number of chro- 

 mosomes, or of more than one maturation mitosis in the partheno- 



genetic generations. 



4. A double series of homologous paternal and maternal chromo- 

 somes runs through the parthenogenetic generations, and the homol- 

 ogous chromosomes are paired side to side in the first spermatocyte, 

 and presumably in the oocyte, of the sexual generation (figs. 10, 22, 

 63, 64, 68, 86, 104, 113). 



5. The first spermatocyte mitosis is the reducing division, sepa- 

 rating homologous chromosomes paired during the prophase. 



6. There are no heterochromosomes of any kind, but the sperma- 

 tids are all alike so far as number, form, and size of chromosomes is 

 considered. 



7. The same parthenogenetic individual may produce : 



(1) All parthenogenetic embryos. 



(2) Parthenogenetic embryos and winter eggs. 



(3) All sexual female embryos. 



(4) All male embryos. 



(5) Parthenogenetic and sexual female embryos. 



(6) Parthenogenetic and male embryos. 



(7) Parthenogenetic, male, and sexual female embryos. 



(8) Male and sexual female embryos. 



