FEMALE ORGANS OF REPRODUCTION 135 



ed from the coil. The lowest coil of the tube is continuous with the vas 

 deferens, which is also twisted, but more loosely. The two vasae meet 

 in the middle line, as in Glossina, to form a common ejaculatory duct, 

 which is of much thinner calibre. Both the vasae and the testicles are 

 of a rich brown colour. There is a pair of accessory glands, not coil- 

 ed, but dilated and bent at the upper end, which open at the junction 

 of the vasae of the two sides. These accessory glands are of a glistening 

 white colour in the fresh state. There are two pairs of such glands in 

 Melophagus. 



The reproductive organs of the female are of special interest in 

 connection with the hereditary transmission of parasites. 



Reproduction among the Diptera takes place, in the majority of 

 instances, by the deposition of eggs and a complete metamorphosis. 



In some, however, the development from egg to larva 



. , ' . The Female Organs 



takes place in the body of the female, and the larva is 



produced either when still young and active or when it is ready for 

 pupation. The oviparous forms will be discussed first. 



The essential organs of the female are the ovaries, each of which 

 consists of a number of ovarian tubes, or ovarioles. The ovarioles open 

 into an ovarian duct on each side, the ducts of the two sides uniting to 

 form a common channel. This in turn leads into a short cavity known 

 as the bursa copulatrix, which opens at the genital opening. The 

 spermathecae, or receptacles for the sperms from the male, and the 

 accessory glands, open into the common oviduct. It is the common 

 oviduct which is modified to form a receptacle for the larva when it 

 passes through the whole or a part of its development in the body 

 of the parent. 



The ovaries are rounded or pear-shaped bodies possessing little 

 cohesion or definite shape. The separate tubes of which they are 

 composed are only very loosely attached to one 

 another, the investment of the whole organ consisting 

 of a few scattered muscular fibres continued upwards from the 

 oviduct. Each ovarian tube terminates as a fine filament at the upper 

 end, and the filaments from each tube in the ovary are collected 

 together to form a sort of suspensory ligament, which passes upwards 

 and forwards, and can be traced to the fat body in the region of the 

 heart. This is known as the apical filament. 



The size and shape of the ovaries depend entirely on the condition of 

 the eggs which are developing in them. When the batch of eggs to be 

 laid next is approaching maturity, the ovaries are very large, and may 



