THE CHROMOSOMES OF THE CERCOPHLE. 137 



Aphrophora spumaria has one chromosome distinctly larger 

 than the others in the equatorial plates (Figs. 26-29). Some- 

 times there appear to be two intermediate-sized as in Philcenus, 

 but the cells and chromosomes are smaller and it is consequently 

 not possible to be sure of small differences. The reduced number 

 of chromosomes is 12, and one of these is an odd chromosome, 

 which behaves in the typical way in division, like Phil ecu its 

 (Fig. 33, X). 



THE ODD CHROMOSOME IN THE GROWTH STAGES. 



Similar as these two species are in the number of chromosomes, 

 and the size relations of the chromosomes, it is striking to find the 

 odd chromosome different in the growth stages. In Philcenus, 

 it is sometimes slightly oval in the earliest stages (Fig. 13), but 

 more often round, and always round in the succeeding stages 

 (Fig. 14, X). This is the condition in Clastoptera, Aphrophora 

 quadrangular is, and Aphrophora quadrinotata. On the other 

 hand, Aphrophora spumaria has a very long narrow dark-staining 

 odd chromosome in the early growth stages (Fig. 30), which 

 becomes round only in the stages just before the prophase of 

 the first spermatocyte division (Figs. 31 and 32). Just such an 

 odd chromosome was described by Dr. Stevens for the Harpswcll 

 form. But in Aphrophora spumaria there are no M-chromosomes. 

 So there is variation in the Cercopidae as to the shape of the odd 

 chromosome in the growth stages. 



CHROMOSOMES AND SOMATIC VARIATION. 



The amount of variation in markings in Philcenus spumarins 

 made me suspect that they might be of more than one species. 

 Some had distinct brown lines on the wings, forming a diamond, 

 while others were of a light tan with only a dark streak at the 

 posterior border. As one of the important cytological problems 

 of the present day is to connect chromosomes with somatic 

 variations, I made a careful study of the equatorial plates of 

 different individuals with different markings. The plates of the 

 first spermatocytes of seven differing individuals are shown in 

 Figs. 1-7. There is evidently no clue to somatic variation here. 

 The plates are strikingly alike, each has one largest chromosome 



