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STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-FLY. 505 



gence from the pupal case, and at this time they may be seen 

 copulating. 



1. The copulation of M. domestica appears to have 

 been first described by Keamur (1738). It has been carefully 

 described recently by Berlese (1902) , whose observations my 

 own confirm. The male may perform a few tentative opera- 

 tions before copulation takes place, and these have been mis- 

 taken for the actual act. The male alights on the back of 

 the female by what appears to be a carefully calculated leap 

 from a short distance, and this act seems to indicate a faculty 

 on the part of the fly of being able to judge distance. It 

 then caresses the head of the female, bending down at the 

 same time the apical portion of the abdomen. The male fly 

 is, however, peculiarly passive during the operation, its influ- 

 ence apparently being only tactual, it is only when the female 

 exerts her ovipositor and inserts it into the genital atrium of 

 the male that copulation can successfully take place. When 

 the ovipositor has been inserted into the genital atrium of the 

 male, the accessory copulatory vesicles of the female become 

 turgid and retain the terminal segment in this position, in 

 which the female genital aperture is situated opposite to the 

 male genital aperture at the end of the penis, the latter 

 depending from the roof of the genital atrium. (This will be 

 better understood by reference to the figures of these parts 

 in Part I of this Memoir). The attachment of the penis to 

 the female genital aperture is made still firmer by the dorsal 

 sclerites of the eighth segment of the female and the ventral 

 sclerites of the seventh segment, the so-called secondary for- 

 ceps of the male acting respectively above and below the 

 penis. The fifth ventral segment, or primary forceps of the 

 male, assist the accessory copulatory vesicles of the female in 

 preventing the withdrawal of the ovipositor before the sper- 

 matozoa have been injected into the female genital aperture, 

 by which way they enter the spermathecae. The whole act 

 may be over in a few moments or they may remain in coitu 

 for several minutes. 



The eggs are laid a few days after copulation ; I found 



