The Chromosomes tn Diahrotica 455 



9 is the equatorial plate with the heterochromosome {x) at a differ- 

 ent level from the other chromosomes. Equatorial plates of the 

 second division are shown in Figs. 10 and 11, the heterochromo- 

 some {x) appearing in Fig. 10, and not in Fig. 11. All of the 

 chromosomes divide in this division giving equal numbers of 

 spermatids and spermatozoa containing ten and eleven chromo- 

 somes, respectively. The spermatids (Figs. 12 and 13) contain 

 a chromatin nucleolus (n), which is certainly not the heterochro- 

 mosome, since it is found in all of the spermatids. As the head 

 of the spermatozoon becomes more and more condensed, the 

 nucleolus gradually decreases in size and finally disappears (Figs. 

 14 and 15). The ripe spermatozoon has a very long slender 

 head (Fig. 16) which stains intensely black in contrast with 

 the earlier gray stages (Figs. 14 and 15). 



DIABROTICA SOROR AND DIABROTICA 12-PUNCTATA 



Diabrotica 12-punctata of the eastern United States and Dia- 

 hrotica soror of the Pacific coast states resemble each other so 

 closely that one might easily be mistaken for the other. Both 

 are greenish yellow or yellowish green with twelve black spots 

 on the elytra. Kellogg describes Diabrotica soror as yellowish 

 green and Diabrotica 12-punctata as greenish yellow. The color 

 varies considerably with the age of the beetle. Diabrotica 12- 

 punctata averages larger, shades more on the yellow, and the under 

 side of the abdomen is green or yellow while in Diabrotica soror 

 it is black. The color of the abdomen seems to be the one exter- 

 nal character by which the two species can always be distinguished; 

 for the size, ground color, and size and fusion of spots are extremely 

 variable in both species. 



A small amount of material of Diabrotica 12-punctata was col- 

 lected at Bryn Mawr, Pa., in October, 1906. On examining the 

 sections, it appeared either that the species was polymorphic as to 

 its germ cells, or that there must be Wo or more sub-species or 

 varieties, and possibly hybrids. It was too late to obtain more 

 material of this kind, so, through the kindness of Miss McCracken, 

 a supply of Diabrotica soror was secured for comparison with 



