128 ALICE M. BORING. 



(Fig. 17), and some 9 (Fig. 18), but the odd chromosome is 

 indistinguishable by either size or position. The anaphases show 

 no chromosome lagging behind or behaving in any way dif- 

 ferently from the others. 



The behavior of the odd chromosome necessitates the conclu- 

 sion that Cerastipsocus vennsus has dimorphic spermatozoa. If 

 half of the secondary spermatocytes have one more chromosome 

 than the others, the spermatids and spermatozoa developing 

 from them must also have one more chromosome. The chief 

 interest in this study lies in the fact that it shows the existence 

 of an odd chromosome in a species of the Corrodentia, an order 

 in which it has not before been described, and therefore adds 

 another order of insects to the list of those with sex chromosomes. 



SUMMARY. 



1. The spermatogonial number of chromosomes is 17. 



2. The odd chromosome is condensed in the growth stage, 

 'first as a long beadlike structure, later as one round body. 



3. There are 9 chromosomes in the primary spermatocytes, 

 8 bivalent and one undivided odd chromosome. 



4. The odd chromosome does not divide in the first spermato- 

 -cyte division. 



5. There are 9 chromosomes in half of the secondary sper- 

 matocytes and 8 in the other half. 



6. All the chromosomes, including the odd chromosome, divide 

 in the second spermatocyte division. 



7. Therefore, this species of Corrodentia has dimorphic 

 spermatozoa. 



UNIVERSITY OF MAINE, ORONO, 

 November, 1912. 



