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MONTGOMERY A STUDY OF THE CHROMOSOMES 



The following general deductions may be drawn from the consideration of these 

 facts. Whenever there is an even number of univalent chromosomes in the spermato- 

 gonia, they unite in the synapsis to produce exactly half this number of bivalent 

 chromosomes. When there is an uneven number in the spermatogonia (Alydus eurinus, 

 Harmostes, Protenor, (Edancala) all but one of the chromosomes unite in the synapsis 

 to form bivalent chromosomes, while the odd one remains single. 



(a) Number and Genetic Relationship. 



At the outset of the present study I was particularly interested to determine 

 whether the numbers of chromosomes might afford clues to the relationship of the group 

 of the Hemiptera heteroplera ; that is, to learn, if possible, whether the number would 

 afford a taxonomic criterion. Most of the families of the Hemiptera are very rich in 

 species, however, and I have been able to procure only a few species for study, so that 

 the present beginning must be continued on many more species before .any conclusion 

 can be reached. 



In the Pentatomidce, counting the chromosomes in the spermatogonia, and not 

 including the chromatin nucleoli, we find the number varies between twelve and sixteen, 

 fourteen being most usual ; in the Coreidoe we find twenty in Anasa and Metapodim, in 

 Alydus eleven and twelve, in Harmostes and Protenor eleven. In the Lygceidw, fourteen 

 in Ichnodemus, Peliopelta and Oncopeltus, eleven in (Edancala, and probably twenty- 

 four in Cymus. These were the three families of which the most species were examined. 

 From these numbers it will be seen that there is considerable variation in number for 

 the different species of one and the same family. Accordingly we must conclude either 

 (1) that the number of chromosomes is easily modified and changed, so that it has little 



