AN UNEQUAL PAIR OF HETEROCHROMOSOMES IN 



FORFICULA 



N. M. STEVENS 



Bryn Mawr College 



With Forty-Eight Figures 



In 1906, there appeared in the Zool. Anzeiger, vol. 30, no. 7, 

 a preHminary paper entitled, "Die Spermatogenese von For- 

 ficula auricularia" by Herbert Zweiger, and the same year this 

 author published in the Jena Zeitschrift, vol. 42, a more elabroate 

 paper under the same title. 



Zweiger found a variable number of chromosomes, 24 or 26 in 

 the spermatogonia and 12 to 14 in the spermatocytes. He de- 

 scribed a chromatin nucleolus in the growth stages of the sperma- 

 tocytes; and in some of the first spermatocyte anaphases, a lag- 

 ging pair of chromosomes which he calls " das accessorische Chromo- 

 som." He also states that in some cysts two such are found, 

 making 14 in all. The numerical conditions were constant for 

 each cyst, but not for all cysts of the same testis. In the second 

 spermatocytes he found 12, 13 or 14 chromosomes. 



Carnoy ('85) described the same species as having 10 to 14 

 chromosomes in the spermatocytes. La Valette St. George 

 ('87) found 12 in first and 12 to 14 in second spermatocytes. 

 Sinety ('01) gives the numbers as 24 in spermatogonia and 12 in 

 spermatocytes. These authors did not deal with the question 

 whether or not heterochromosomes are present in Forficula. 



Last summer while I was collecting material at the Marine 

 Station in Helgoland during the third week in July, I chanced to 

 find an abundance of Forficula and identified the insects with the 

 aid of the laboratory collection, as Forficula auricularia. Having 

 previously gone over the question as to heterochromosomes in 



