TYPES OF SPECIES OF CESTODA— KHEFFT. 17 



pore-bearing side. They are situated at a rather lower dorso- 

 ventral level on this side than on the opposite side, a feature 

 similar to that found in other species of Diorchis. Transverse 

 vessels were not seen. There appears to he a valve-like projection 

 into the lumen of each ventral vessel near the posterior edge of 

 each segment (PI. ii., tig. 4). 



Genitalia. — The genital apertures are unilateral, being located 

 on the right side. They lie marginally in front of the middle of 

 the edge, being usually at the junction of the anterior third with 

 the posterior two-thirds. A distinct papilla is absent. There 

 may be a very short narrow common genital cloaca into which 

 the male and female apertures open, the female pore being 

 immediately below that of the male system. As already remarked 

 the genital canals pass above the longitudinal nerve and both 

 excretory vessels. 



The male organs consist of two large testes placed more or 

 less symmetrically in the posterior portion of the segment. They 

 appear early but develop slowly for a considerable distance back 

 from the anterior end, when they begin to increase very suddenly 

 in size at the time of male maturity. They then occupy a large 

 part of the medulla lying between the excretory vessels, the 

 diameter of each being almost OT mm. Sometimes they are 

 quite close together, especially in all the younger segments 

 (PI. ii, tig. 5), but with increasing size of the glands and the 

 seminal vesicle their symmetrical arrangement becomes disturbed 

 (PI. ii., fig. 6). A large mass of spermatozoa comes to be stored 

 in the vesicula seminalis after which the male glands commence 

 to dwindle rapidly, the female organs meanwhile coming to 

 maturity. The vesicula in ripe segments is a large rounded 

 structure lying near the dorsal surface in the anterior portion of 

 the segment. Its position is seen to vary, being usually above 

 and in front of the testes which is remote from the genital pore 

 in young segments but in proglottids which have reached male 

 maturity it usually lies rather nearer the midline separating the 

 two glands. A much narrower tube connects the vesicula with 

 the cirrus sac. The cirrus sac is a long, more or less tubular, 

 slightly twisted structure of from 0-270 to 0'35 mm. in length, 

 with a maximum breadth of about - 050 mm., lying dorsally in 

 the anterior portion of the segment. The broadest part is towards 

 its inner end, the other end being much narrower (0-03 mm.). 

 The organ stretches inwards almost to the midline, and occasion- 

 ally much further. Its musculature is somewhat thicker around 

 the middle. There is a small seminal vesicle within the sac. 



9, 



