The Chrotiiosonies in Diahrotica 463 



over it is perfectly possible for more than four to occur in either 

 male or female, as will be seen from the tables on p. 8, 



DISCUSSION. 

 Sex Determination 



For the present it is necessary to assume that the number of 

 chromosomes in the female bears the same relation to the number 

 in the male as in other cases among the Coleoptera and Hemiptera 

 where an odd or unpaired heterochromosome is present in the 

 male. The division products of the unpaired chromosome pass 

 to one-half of the spermatozoa and these spermatozoa fertilize 

 the eggs which develop into females; while the spermatozoa 

 which lack the odd chromosome fertilize the eggs which produce 

 males. This still seems to be as far as we can safely go in dis- 

 cussing the relation of the odd chromosome to sex determination. 

 This chromosome is uniform in its behavior in the three species 

 of Diabrotica, and it seems clear that it alone of the heterochro- 

 mosomes described can have any connection with the determina- 

 tion of sex. 



The" Supernmnerary ' Chromosomes 



The small heterochromosomes in Diabrotica 12-punctata were 

 first seen in some first spermatcoyte spindles by Miss Anne M. 

 Lutz of the Carnegie Institution of Experimental Evolution, 

 Cold Spring Harbor, more than two years ago, but the matter 

 was not followed up. 



Prof. E. B. Wilson, in a recent communication (Science, n. s., 

 vol. 26, no. 677, p. 870), has given the name "supernumerary" 

 chromosomes to certain additional heterochromosomes in Meta- 

 podius (Hemiptera), and perhaps that name is as good as any 

 other for the additional small heterochromosomes which appear 

 in variable numbers in about 50 per cent of random collections 

 of Diabrotica soror and Diabrotica 12-punctata. As in Meta- 

 podius the number of supernumeraries is constant for the individ- 

 ual. In Metapodius the supernumeraries are described as accom- 

 panying a pair of idiochromosomes with which they frequently 

 unite to form a compound element in the second spermatocyte. 



