CHROMOSOME NUMBERS IN METAZOA 67 
A third set of heterochromosomes are the m-chromosomes, 
small chromosomes which remain condensed in the growth period 
and conjugate late. These are characteristic of the coreid Hem- 
iptera and occur in some of the Lygaeidae; they accompany an 
unpaired X except in Metapodius and Ichnodemus where they 
accompany an XY. 
Finally there are those chromosomes which are normal in beha- 
vior but consist of unequal parts. To this class belong the d- 
chromosome of Nezara hilaris and the compound chromosome 
of Notonecta insulata, which divide equally in the two divisions, 
and the unequal tetrads of some of the Orthoptera which divide 
into unequal parts in one division: Schistocerca (Hartmann, 
13); Acridium granulatus, Tettigidea parvipennis (Robertson, 
16); Arphia, Dissosteira, Brachystola (Carothers, 713); and Phry- 
notettix (Wenrich, ’16). 
Princeton, N. J. 
December, 1918. 
