Vol. XXIV. February, /p/j. No. 



BIOLOGICAL BULLETIN 



THE ODD CHROMOSOME IN CERASTIPSOCUS 



VENOSUS. 1 



ALICE M. BORING. 



Many groups of insects belonging to the species Cerastipsocus 

 venosus were found on one ash tree near the laboratory at Woods 

 Hole last summer. As they belong to the Corrodentia, an order 

 of insects in which the chromosome history has not yet been 

 worked out, it seemed worth while to study the spermatogenesis. 

 They are gregarious in habit and not strong flyers. In the 

 middle of August there were still many nymphs, but they all 

 soon developed wings and by September i had all flown from 

 the ash tree. The material used was partly from nymphs and 

 partly from adults. The males are slightly smaller than the 

 females, and both nymphs and adults furnished the entire series 

 of stages for the study of the spermatogenesis. The spermato- 

 genesis falls into line with that of many insects in other orders. 

 There is an odd chromosome that does not divide in the first 

 spermatocyte division. 



METHODS. 



The testes are small trilobed organs, resembling clover leaves, 

 situated dorsally, one each side of the anterior end of the 

 abdomen. The most of this study was made from acetocarmine 

 preparations , but compared with material fixed in Gilson or 

 Flemming and stained in iron haematoxylin or thionin. The 

 small testis was put whole in a drop of Schneider's acetocarmine 

 on a slide, left there a couple of minutes, covered with a cover- 

 glass, pressed flat, all extra acetocarmine was drawn off with 



1 I wish to express my thanks to Dr. Pearl for criticizing the manuscript of this 

 and the following paper, to the Director of the Marine Biological Laboratory for 

 the facilities offered me at Woods Hole, and to Mr. Nathan Banks and Mr. E. P. 

 Van Duzee for identifying the species. 



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