1906.] The Internal Anatomy of Stomoxys. 



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of some 60 ovarioles. The ovary is moored to the body wall by a profusely 

 branching trachea, which arises from the pleural space and ramifies among the 

 ovarioles. In the natural position the ovaries lie with the long axis of the 

 ovarioles pointing upwards towards the dorsal surface. Each ovariole 

 contains never more than four ova in various stages of development. 



The ovaries vary in size according to the degree of maturity of the lowest 

 ova. In some flies they occupy more than half of the whole abdominal space. 

 The ovarioles open into a wide tubular duct which joins its fellow from the 

 other ovary like the upper limbs of a Y. As a result of this junction is formed 

 the common oviduct (fig. 3, CO.), which runs down, forming a long third limb 

 to the Y. Below the attachment of the uterine appendages the oviduct 

 continues as the uterus. 



The appendages consist of the uterine glands and the receptacula seminis. 

 The uterine glands (fig. 3, TJ.Gv) are two rather stout tubular organs with 

 slightly bulbous extremities. The bulbous end is firmly joined to the lateral 

 oviduct by a very short double strand of connective tissue. Each gland ends 

 in a short fine duct, and these ducts enter separately the shallow constriction 

 which forms the arbitrary division between the oviduct and uterus. 



The receptacula seminis (fig. 3, U.S.) are two small, black, spherical bodies, 

 each with a cellular socket resembling the fitting of an acorn cup. From 

 this runs a very fine duct which enters the division between the oviduct and 

 uterus in the mid-dorsal line. The receptacula are attached to each other, 

 but can be separated by dissection. The distal portions of the two ducts are 

 quite separate, but later each duct enlarges slightly, and from this point on 

 to its insertion is closely attached to its fellow. This portion can, however, be 

 separated by dissection, and it is then seen that the ducts are distinct and 

 enter separately. 



The uterus (fig. 3, U.) is a tube of the same diameter as the common 

 oviduct above, and runs down in the middle line into the ovipositor. The 

 ovipositor (fig. 3, O.P., and fig. 4) consists of three cylindrical segments of 

 thin chitin, which usually lie telescoped inside the abdomen. There is also a 

 single external flap of dark chitin which lies folded up on the ventral surface 

 of the fly. When the ovipositor is extruded by squeezing the fly's abdomen, 

 the receptacula and uterus are pulled down with it, and can be seen through 

 the transparent walls. 



The upper segment of the ovipositor has three narrow ribs of dark chitin in 

 its long axis, two dorsal and one ventral. The next segment is similar. The 

 last segment has two dorsal plates only. The external flap, which is probably 

 the third rib of the last segment, is, roughly, quadrilateral, and has two 

 divergent prong-like processes arising from its free border. 



