A PRELIMINARY ACCOUNT OF THE CHROMOSOMES 



IN THE EMBRYOS OF ANASA TRISTIS AND 



DIABROTICA VITTATA. 



WILLIAM E. HOY, JR., 

 PRINCETON UNIVERSITY. 



It was suggested to the writer, in 1912, by Prof. E. G. Conklin 

 that a comparative study be made of the chromosomes in the 

 somatic cells of certain insects, as contrasted with the sex cells. 

 The first material was collected during the following summer, and 

 included embryos of Anasa tristis and Diabrotica vittata. Mate- 

 rial of a number of other forms, not restricted to the Insecta has 

 since been collected and examined to some extent. The results 

 obtained from the latter, together with a more extended account 

 of the forms briefly described here, will be discussed at greater 

 length in another paper. 



Embryos of Anasa tristis were obtained covering a period of 

 development from the incomplete blastoderm stage up to about 

 the time of hatching. Some difficulty was experienced in obtain- 

 ing the eggs of Diabrotica vittata, but fortunately the stages ob- 

 tained extend from the second maturation division up to the 

 segmentation of the embryo. 



Anasa tristis. In 1906, Wilson in his "Studies on Chromo- 

 somes," Part III., gave the results of his work on the spermato- 

 genesis of Anasa tristis. There are twenty-one and twenty-two 

 chromosomes in the spermatogonia and oogonia, respectively. 

 Of the twenty-one chromosomes in the spermatogonia, twenty 

 can be paired. There is, here, a marked differentiation in the 

 size of the chromosomes. In each plate there are three large 

 or macrochromosomes, and two small or microchromosomes. 

 The unpaired or .r-chromosome (idiochromosome; accessory 

 chromosome) is one of these three largest chromosomes, although 

 it cannot be exactly determined which one it is. The two 

 microchromosomes have been termed the w-chromosomes. In 

 the second maturation division the rv-chromosome moves un- 



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