38 



THE NORTH AMERICAN SPECIES OF DROSOPHILA. 



the Drosophilinae occurs also in Scatophaga (Cordylurinae), and appar- 

 ently in Parydra (Ephydrinae) . The two receptacles of Chiromyia 

 minima Becker (Geomyzinae) are similar in structure to those of 

 Aulacigaster leucopeza. 



Table 2. 



' Aulacigaster (3 receptacles) and Seoptera (4 receptacles) each have only two ducts. 



The ovaries consist of five or more egg-strings each. At the anterior 

 end of each string lie the oogonial cells; at the posterior end is a 

 mature egg. The region between is filled with eggs in intermediate 

 stages of development. After oogonial multiplication has been com- 

 pleted there are found to be cysts of oogonial cells surrounded by 

 follicular envelopes. Each cyst contains 16 nuclei, of which one 

 becomes the egg-nucleus and the other 15 belong to nurse -cells. 

 These 16 nuclei are alike to all appearances until a relatively late stage.* 



* This account of the ovary is from Plough (1917). 



Since this paper was sent to press J. F. Nonidez (1920. Biol. Bull. 39: 207-230) has pub- 

 lished a full account of the structure and physiology of the internal genital apparatus of both 

 sexes oi Drosophila melanogaster. 



