16 TROPICAL MEDICINE AND HYGIENE 



obliquely the opening of a sac the spermatheca, or 

 receptaculum seminis in which the spermatozoa are 

 stored up. A second tube leads into the ovarian tube 

 from the dorsal aspect of the worm, and is known as the 

 canal of Laurer. The function of this tube is not clearly 

 understood. 



The ovarian tube, after the junction of these tubes, is 

 dilated, and surrounded by a mass of glands, the shell- 

 glands. Into this dilated portion of the ovarian tube two 

 ducts open, those of the much branched yolk-glands 

 vitellaria which are situated near the lateral edges of the 

 worm. In the dilated portion of the ovarian tube the 

 ootype the ova are fertilized by the spermatozoa, which 

 are discharged from the spermatheca. They also receive 

 the abundant yolk-masses and are provided with a shell 

 or envelope. 



From the ootype the eggs pass through a convoluted 

 tube the uterus. This opens externally at the genital 

 pore, which is situated on the ventral aspect (fig. 4). 



Though most of the trematodes are hermaphrodite, 

 copulation of two individuals is the rule. This may take 

 place either by the injection of the spermatozoa ot one 

 individual into the uterus of another, or, according to 

 some, through the canal of Laurer. Auto-fertilization 

 may take place, as the openings of the male and female 

 organs, though separate, are close together. 



The digenetic trematodes are divided into two great 

 divisions : (i) Those which are hermaphrodite, male and 

 female organs in the same individual the Fasciolidw, 

 Paramphistomidce, &c. ; and (2) those in which the male 

 and female organs are in separate individuals Schisto- 

 somidce. 



