Ii8 N. M. Stevens 



within one prospective second spermatocyte, (Fig. 27) and all 

 intermediate stages. In the first spermatocytes there are four 

 large chromosomes of about equal size and two small ones (Fig. 

 28). In the prophase of the larger second spermatocytes one of 

 the four large chromosomes is larger than the others (Fig. 29)- 

 This is as far as the evidence goes for this species. 



On restaining a pale sHde of the Harpswell willow aphid, one 

 cyst of second spermatocytes in metaphase was found. Here the 

 two sizes of cells could be distinguished and chromosomes counted 

 (Figs. 30 and 31). Fig. 32 shows daughter plates of a second 

 spermatocyte in anaphase. Figs. 33 and 34 are prophases of 

 spermatogonial mitoses from a male embryo. Only five chromo- 

 somes could be counted. It was impossible to determine the 

 number in metaphases in the same embryo. This material, if it 

 could be secured in abundance, should give perfectly clear and 

 decisive results on all points connected with the heterochromo- 

 some, but I found it only on one small willow at South Harpswell 

 Me., and have discovered nothing like it anywhere else. 



In the black aphid on the common milkweed there are four 

 chromosomes in the first spermatocytes, the third largest staining 

 darker in pale iron haematoxyhn preparations (Fig. 35). Fig. 

 36 is an early anaphase showing two double chromosomes and 

 the single elongating heterochromosome (x). Fig. 37 is a pro- 

 phase from the same preparation. Figs. 38, 39 and 40 are dif- 

 ferent stages in the division of the first spermatocyte. The num- 

 ber in the small second spermatocytes was not clear, but in a 

 similar aphid from the garden nasturtium these cells have three 

 chromosomes while the larger ones have four (Fig. 41). 



The woolly aphid from the beech shows well how deceptive 

 the anaphase of the first spermatocyte can be. Fig. 42 is the 

 stage most often seen, while Fig. 43 shows the final result of 

 division. Figs. 44 and 45 are from the Saranac willow aphid, in 

 which both cell and heterochromosome simulate equal division, 

 but in the final stages of mitosis the whole heterochromosome 

 goes over to one cell and the other cell becomes only slightly 

 smaller. 



In my '06 paper, PI. IV, a few figures (110-113) were given for 



