12 STUDIES ON THE GERM CELLS OE APHIDS. 



The Pea Aphid. 



The pea aphid, or pea louse, as it is commonly called, shows a 

 very neatly paired double series of eight chromosomes in the parthen- 

 ogenetic generations. Figure 114 is from a maturation spindle and 

 figures 115 and 116 from a 32-cell stage of the parthenogenetic egg. 

 The sexual forms were not available for study. 



The Goumi Aphid. 



On the shrub known as the goumi is found an interesting aphid of 

 which I discovered the sexual forms too late to get anything of the 

 spermatogenesis or to find the parthenogenetic forms. The males 

 were small and nearly black; the females of three distinct colors — 

 green, red, and yellow — but all were marked alike with a darker stripe 

 on the back. When brought into the laboratory they laid their 

 orange-colored eggs in abundance on a white cloth tied over the jar 

 in which they were confined to prevent their traveling all over the 

 laboratory. 



Figures 117 and 118 show polar bodies containing five chromo- 

 somes, and figure 119 the male and female pronuclei in contact, the 

 female nucleus being the larger and containing two plasmosomes (/>). 



Figures 120 a and 120^ show a prophase of mitosis from an 8-cell 

 stage. Such stages are of course not so good for comparison of the 

 chromosomes as the equatorial plate, but the two series of homolo- 

 gous chromosomes are fairly well shown, considering that they do 

 not all lie in the same plane or even exactly parallel with the surface 

 of the section. 



In many cases more stages might have been figured, but it did not 

 seem advisable to multiply figures more than was necessary to show 

 the characteristic appearance and behavior of the chromosomes of 

 each species. Several drawings of the same stage have often been 

 given to show the variations in arrangement of the chromosomes. 



