AND HABITS OF THE YELLOW DUNG- FLY. 



635 



Female Genitalia and Method of Oviposition. 



As seen externally, the apex of the abdomen of the female ends 

 in two setiferous lobes (text-fig. 3, a), between which the anus 

 opens. Below this again is the retractile ovipositor (text-fig. 3, h). 

 This consists of a pair of chitinised blades attached, proximally, 

 to a membranous tube. The whole of this can be retracted within 

 the abdomen. The blades are pointed and, when placed together, 

 form a groove. The common oviduct, which is very large, opens 

 into it. 



When oviposition is about to take place, the abdomen is 

 stretched out horizontally Avith the ovipositor extruded. In this 

 position an egg is passed down into the groove formed by the 

 juxtaposition of the two blades of the ovipositor. Ovipositor 

 and egg are tlien pressed down into the dung obliquely. The 

 blades are pulled apart a.nd the egg released. 



Text-figure 3. 



y^^^'^s^ — 



Abcioraen of female S. stercoraria, witli genitalia extended. 



The eggs are more or less scattered over the surface of the 

 dung, but ten or fifteen or more may be deposited in one small 

 area, particularl}^ where there is a crack or a crevice where the 

 softer parts of the dung are exposed. 



Fresh dung is preferred by the females for oviposition, but 

 occasionally eggs are laid in dung a week or more old. In this 

 case the crust on the surface of the duug is too hard for the ovi- 

 positor to be inserted deeply, and eggs are often seen only half 

 buried. This does not prevent the egg from hatching, but the 

 larva usually has difiiculty in getting through the hardened crust 

 of the dung. 



Oviposition occasionally takes place with the male in situ, in 

 which case the male removes his abdomen from that of the 

 female, and, instead of clasping her with his two front pairs of 

 legs, drops back clasping her only with the front pair. The 

 female then can manipulate her abdomen freely whilst the male 

 follows her about. 



When a female is gravid, the abdomen is so distended as to 

 make her practically incapable of flight. The abdomen is re- 

 duced to nearly a fourth its size when oviposition has taken 

 place. 



42* 



