PARASITES OF ANIMALS. 103 



another larger sucker (6), with no opening at its bottom ; 

 just in advance of this there are situated, side by side, the 

 male and female genital orifices (c). The external male 

 organ is long, slender, and when protruded is curved in a 

 spiral. It can be retracted into a small cavity. 



Anatomy. 



The reproductive system is very largely developed and com- 

 plicated. The male organs, or testicles, consist of large 

 clusters of vermiform, convoluted, yellowish tubes, situated 

 in the middle region of the body, and filling up about one- 

 half of the whole interior. The female organs, for they are 

 hermaphrodites, are also largely developed and complicated. 

 The lateral and hinder parts of the body are filled with in- 

 numerable, very small, yolk-sacks, which communicate, by a 

 complicated system of branched ducts, with a heart-shaped 

 ovary, and this in turn has a short duct leading to the uterus- 

 like organ, which consists of a convoluted, wide tube, forming 

 a sort of rosette behind and around the ventral sucker. The 

 uterine tubes show through the skin and are brownish yellow, 

 owing to the numerous minute eggs with which they are filled. 

 These eggs are discharged, one by one, from the small ex- 

 ternal orifice as fast as they become mature. The mouth 

 communicates with a small dilated oesophagus, and this gives 

 rise to two large intestinal tubes, which diverge in advance of 

 the genital orifice and extend backward, along each side, to 

 near the posterior end, sending off numerous lateral branches, 

 which again subdivide into many short divergent branchlets, 

 as shown in Figure 73, d. The branches of these digestive 

 tubes are all closed at the ends, and they communicate with 

 the exterior only through the mouth. In life these tubes are 

 all filled with food, consisting chiefly of bile, with some blood- 

 corpuscles, etc. Another system of numerous, arborescently 

 branched tubes is found nearer the dorsal surface, and as they 

 show through the skin, on that side, they may be examined 



Figure 73. Fasciola hepatica, natural size, seen from below ; a, mouth and 

 oral sucker ; b, ventral sucker ; c, genital orifice ; d, branches of intestine. From 

 Cuvier. 



