The Chromosomes in Diahrotica 461 



There were no spermatogonia! plates of type lie and IIo' which 

 could be counted, and in no case, though many ovaries have been 

 fixed and sectioned and others examined with aceto-carmine, has 

 it been possible to determine the number and character of the 

 chromosomes in the female. 



DIABROTICA I2-PUNCTATA 



Exactly the same conditions as to the small heterochromosomes 

 prevail in Diabrotica 12-punctata collected at Bryn Mawr, Pa., 

 as in Diabrotica soror at Mountain View, Cal. Out of the 

 first 100 males examined in October, 1907, 51 had no small hete- 

 rochromosome, 35 had one, 11 had two, 2 had three and i had 

 four, while in Diabrotica soror the numbers for the five corre- 

 sponding classes were 48, ^1^, 15, 3, i. 



A few figures only will be given for Diabrotica 12-punctata. As 

 in many other Coleoptera, spermatogonia! equatorial plates in 

 which the chromosomes are well enough separated for accurate 

 counting are rarely found. The one shown for Diabrotica soror, 

 type \\h, in Fig. 49, was drawn from an aceto-carmine prepara- 

 tion in which the chromosomes had been separated by pressure 

 on the cover-glass. Figs. 66 and 67 are spermatogonia! plates of 

 Diabrotica 12-punctata, type I and type \\a, drawn from sections. 

 There is some overlapping here, but no doubt as to the number 

 in either plate. Growth stages for the five classes are shown in 

 Figs. 68, 69, 70, 71 and 72. The larger size of both nucleus and 

 chromosomes in Fig. 72 is due to its having been drawn with the 

 same power from an aceto-carmine preparation. These figures 

 also serve to show something of the diversity of form of the odd 

 chromosome (x). When no small heterochromosome is present 

 it usually is nearly spherical (Figs. 18 and 68). Where one or 

 more of the small chromosomes are found, it is as a rule somewhat 

 elongated (Figs. 69 and 70), often irregular in form (Fig. 72), or 

 much elongated and bent in U-form. Whether this difference 

 indicates some influence exerted by the presence of the smaller 

 heterochromosomes, or marks the individuals containing the small 

 chromosome as a separate species is not at present clear. 



