ANATOMY OF MONOPYLIDIUM PASSERINUM, FUHR. 409 



female parts. Its course here may be straight or some- 

 what zigzag. In the region of the receptaculum seminis 

 it becomes very considerably coiled, and on passing further 

 forwards the loops become larger while the walls become 

 strongly muscular. The tube now appears as a large twisted 

 mass stretching from the inner end of the vagina or even 

 further back, to the anterior border of the segment. In 

 section this deeply staining structure is seen to occupy the 

 whole of the mid-region of the medulla in the dorso- ventral 

 plane. In all segments examined the windings were much 

 larger and more extensive in their distribution than is 

 shown in Fuhrmann's figure, this being, no doubt, due to 

 the quantity of contained spermatozoa. The vas deferens 

 ultimately passes postero-laterally to enter the cirrus sac. 



The cirrus sac is an elongate spindle-shaped organ, or 

 it may even be roughly tubular. Its length is from 0*17 

 to 0*20 mm., with a maximum width of 0*04 mm. In 

 segments where the cirrus appears everted, the sac assumes 

 an almost spherical form of 0*05 mm. diameter. The male 

 aperture is situated just in front of the female opening, the 

 cirrus sac passing inwards, forwards and somewhat ven- 

 trally and lying at about the same dorso- ventral level as 

 the vagina, both being situated just above the displaced 

 ventral excretory vessel and lateral nerve. Near the 

 middle of the anterior part of the segment, it takes up the 

 vas deferens. The muscular walls of the sac enclose a 

 coiled cirrus which is capable of considerable eversion, in 

 some cases measuring at least 0*126 mm. with a breadth 

 of 0*04 mm. As Fuhrmann has already pointed out, the 

 cirrus is covered with a very delicate bristling. 



Female genitalia.— The female complex as a whole, 

 occupies a rounded zone near the centre of the segment. 

 The ovary is distinctly two-winged, each part forming a 

 somewhat rounded mass. The " wings" are connected by 



