586 



T RE MA TO DA 



taking origin at the posterior end, runs forward to join with the vitellarian 

 duct from the single yolk gland, which lies about the middle of the body. 

 The junction of the two ducts is at first narrow and surrounded by the shell 

 gland, but it soon dilates into the uterus, which runs forwards to end in the 

 genital pore, just behind the ventral sucker. The eggs are bluntly spindle- 

 shaped, yellowish in colour, slightly transparent, and provided with a thin 

 shell, without a lid, but possessing a terminal spine, which may be absent 

 at the posterior end. They measure from o-i2 to O'lg millimetre in length 

 and 0'05 to 0-073 rnillimetre in breadth, but vary considerably. 



Life-History. — ^The young immature and mature males and 

 females are found in the portal system. 



Looss notes that it is not uncommon to find males alone in the 

 portal vein, and, further, that they are all of the same age. 

 Eventually they pair, and now the male carries the female along 

 that vein down the inferior mesenteric vein to the bladder, which 

 is a fairly direct route, but Looss considers that they may be 

 chemically attracted to the bladder, for their journey is against 

 the blood-stream, and they are enabled to perform it by means 

 of the bristles on the male cuticle. , 



The length of time occupied by the journey is not known, and 

 probably varies considerably. Arrived in the veins of the bladder, 

 the real oviposition begins, and Looss is inclined to think that the 

 female can push the head (close to which is the genital opening) into 

 the capillaries, and thus lay the eggs directly into these channels, 

 where they are held in position by contraction of the capillary upon 

 them. Looss thinks that it is probable that the worms may live 

 three years in these vessels, producing during that period large 

 numbers of eggs, which work their way like any other foreign body 

 into the lumen of the bladder, probably by means of the con- 

 tractions of that organ . 



Leiper finds that in experimentally infected monkeys eggs begin 

 to appear about ten weeks after infection. 



Egg.— During their journey through the tissues the eggs increase 

 in size from o-o8 to 0-09 in length and 0-03 to 0-04 fj, in breadth 

 in the ootype to 0-13 to 0-15 ju in length and 0-04 to o-o6 fi in breadth 

 in the urine, while the embryo develops, so that when they are 

 voided in the urine they contain a well-developed miracidium; but 

 during this journey many die and become calcified. It is not 

 Icnown how long an egg must take before it escapes in the urine, 



Fig. 228. — Bullinus contortus 



MiCHAUD, 1829, 



Fig. 229. — Bullinus dybowskii 

 Fischer, 1891. 



