132 ETHEL NICHOLSON BROWNE 



these lead, of course, to those forms, of which there are probably 

 many, where there is never a visible dimorphism in the chromatin 

 content of the spermatids; and yet there is reason to believe that 

 such a dimorphism exists. This important fact has been pointed 

 out by Wilson in considering Oncopeltus, and additional evi- 

 dence is given by the same phenomenon in N. shooterii. There 

 is absolutely no question in this case of the existence of an X Y 

 pair, as these chromosomes are typical and constant in position 

 and behavior in all the species of the genus thus far examined. 



VI. THE CHROMOSOMES OF N. INDICA 



N. indica has the same number of chromosomes as N. undulata 

 and N. shooterii, and they are arranged in the first division some- 

 what like those of N. undulata, but slightly modified. 



a. Observations 



In N. indica, there are two small chromosomes in the center, 

 as shown by spindles in side view (fig. 81). Owing to the prox- 

 imity of these two chromosomes and to the fact that one pair 

 divides in advance of the other, they most frequently appear 

 arranged in a linear series (fig. 82). This appearance is common 

 in N. undulata also. Three other very characteristic chromo- 

 somes appear in side view, two of these being large compound 

 chromosomes, similar to the largest chromosome of N. glauca, 

 only smaller, and a third chromosome, largest of all which con- 

 sists of a main body and usually a small piece on either side, 

 looking like a compound chromosome, made up of one large and 

 two very small parts. This chromosome can be traced through 

 from early prophase of the first division to the telophase of the 

 second by its characteristic shape, and is the larger component 

 X of the X Y pair. The double chromosomes and the X chro- 

 mosome are shown as they lie on the spindle in figures 83 and 

 84. A complete set of chromosomes as seen in side view gives 

 a total of 14, including X, the two doubles and the two small 

 ones in the center (fig. 85 A, B, C). Polar views showing the 

 complete number 14, the general grouping and the size relations 

 are given in figures 86 to 88. The arrangement seems somewhat 



