CHROMOSOMES. 



39 



VII. CHROMOSOMES. 



The chromosomes of various species of Drosophilinse have been 

 studied by Miss Stevens (1908), Bridges (1916), and Metz (1914, 1916). 

 The two most striking general facts brought out by these studies are, 

 first, that as a rule division figures are more easily obtained in ovarian 

 tissue than in testicular; and second, that the two members of each 

 pair of chromosomes commonly lie side by side at all cell divisions. 

 This latter characteristic is found in most, if not all, other Diptera as 

 well as in the Drosophilinse . 



II A Mb Mc II d 



II H Up " 



«H 





II o 



II II 



^ 



)0 »^(( 



^» t. 



ni 



Fig. 44. — Diagram of chromosome groups 

 found in the Drosophihnae (after Metz). 



Metz has described and figured the chromosome groups of a large 

 number of species of the subfamily. He recognizes twelve different 

 types, which are shown in figure 44, a diagranmiatic representation 

 made by Metz. The various types are represented by the following 

 species : 



In types I, J, K, and L the male and female groups are both shown, 

 and these obviously differ with respect to one pair — the sex chromo- 



