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STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-FLY. 431 



There is a single pair of accessory glands (ac.g.}, which are 

 fairly long, and on nearing the vagina they become narrower 

 to form a slender duct, which opens on the dorsal side of the 

 vagina immediately behind the ducts of the spermathecao. 

 The accessory glands are closely united with the fat-body. 

 They probably secrete the adhesive fluid which covers the 

 eggs when they are laid, and causes them to adhere to each 

 other and to the material upon which they are deposited. 

 Behind the accessory glands there is a pair of thin-walled 

 transparent vesicles (tasche dell' ovid utto of Berlese), 

 which I propose to name the accessory copulatory vesicles 

 (a.c.v.) on account of the part they take in ensuring firm 

 coitus with the male during copulation, during which process 

 they expand to a much greater extent. 



The ovipositor (fig. 8). The terminal abdominal segments 

 of the female are much reduced to form a tubular ovipositor, 

 the chitinous sclerites being reduced to form slender chitinous 

 rods. When extended it equals the abdomen in length. It 

 is composed of segments vi, vii, viii, arid ix, each being sepa- 

 rated from the adjacent segments by an extensible inter- 

 segmental membrane, which is covered with fine spines. 

 When the ovipositor is retracted (fig. 23, ovp.) it lies in the 

 interior of the posterior end of the abdomen, the segments 

 being telescoped the one within the other, so that only the 

 terminal tubercles are visible from the exterior. The dorsal 

 arch of the sixth abdominal segment is reduced to a A-shaped 

 sclerite (vi, d.) } lying on the dorsal side of the segment. 

 The ventral arch of this segment is reduced to a slender 

 chitinous rod (vi, v.) in the mid-ventral line. The dorsal 

 arch of the seventh segment is represented by two slightly- 

 curved sclerites (vii, d.), with their concave faces opposite ; 

 the ventral arch (vii, v.) is similar to that of the sixth 

 segment. At the junction of the posterior ends of the 

 sixth and seventh segments with the inter-segmental mem- 

 branes succeeding them there are several setose tubercles 

 arranged more or less in pairs, but they vary in development 

 in different individuals. The dorsal arch of the eighth 



