Studies on Chro?riosomes 



93 



aries accompany a typical pair of unequal idiochromosomes (as in Type II). In 

 other forms (Diabrotica), the supernumeraries accompany an unpaired idiochromo- 

 some (as in Type III). In these cases definite numerical formulas cannot be 

 given, since the distribution of the supernumeraries is variable and both sexes show 

 a variable number of chromosomes in consequence (directly known only in Meta- 

 podius.) For the present these cases may most conveniently be treated as sub-types 

 as follows: 



Ila 

 Forms that agree with Type II except that certain individuals may possess, in 

 addition to a pair of idiochromosomes, one or several supernumerary chromosomes. 

 The cases described, with the numbers of chromosomes observed, are as follows: 



* This number occurs only in Montgomery's ('06) material of this species, identification of which 

 though probably correct, is not absolutely certain. This case will be considered in a later publication. 



Ilia 



Forms that agree with Type III except that certain individuals may possess, in 

 addition to an unpaired idiochromosome, one or several supernumerary chromo- 

 somes. Described cases as follows: 



