EXAMINATION OF HELMINTHES 137 



terminal portion of the uterus, between the ventral sucker and the 

 bifurcation point of the stomach-tubes, a whitish, crooked body is seen. 

 This is the cirrhus pouch, and in dead specimens a portion of the 

 cirrhus is usually extruded from it. The boundary between the field 

 occupied by the uterus and that occupied by the testes is formed by 

 the yolk-ducts, which, when filled with yolk-cells, appear as white 

 threads running transversely of the body. The longitudinal yolk- ducts, 

 which occur in the neighbourhood of the yolk-glands and run parallel 

 to the margin of the body, will also appear as white threads if they 

 contain yolk-cells'. At a point in the middle line, the transverse yolk- 

 ducts combine to form a short irregular tube, running towards the 

 head end of the body. This is the yolk receptacle, and in front of it 

 is the shell-gland (" Mehlis' body "), which appears as a whitish disc, 

 about 1*5 mm. in diameter, and is composed of numerous pear-shaped 

 cells arranged radially. 



The details of the internal structure will not be seen with equal 

 clearness in every fluke, but by examining several specimens the 

 student will find that he is able to identify all the organs described 

 above. Owing to its position, the ovary is rarely distinguishable in 

 the living object. It is a ramified body, lying in front of the right 

 horizontal yolk-duct, and is hidden partly by the folds of the uterus 

 and partly by the follicles of the yolk-gland. 



The distinguishing features of the liver-fluke with regard to form, 

 armature and position of the suckers and of the genital opening, course 

 of the uterus, pronounced development of the yolk-glands, ramification 

 of the intestine, testes and ovary, and the exact duplication of the 

 internal organs on either side of the body, may be taken as typical of 

 the genus Fasciola as it is at present defined. These characteristics 

 should be compared with those of Dicrocceliutn and Opisthorchis, as 

 well as with those of the genera of which the intestinal Trematodes 

 of frogs are typical examples. 



The stomach-tubes and excretory system of fresh flukes may be 

 injected with Prussian blue or other cold substance. The best instru- 

 ment for this purpose is a glass tube drawn out at one end to a fine 

 point, which, when filled with colour, is inserted into the oral sucker 

 and pressed down into the pharynx. The mass is expelled by means 

 of an india-rubber ball attached to the large end of the tube, or by 

 blowing down it until the organs are filled. The beginner is very 

 liable to push the point of the glass tube too far down into the 

 pharynx and pierce the oesophageal wall. In this case the stomach- 

 tubes will remain empty, but the excretory system will, as a rule, 

 become filled. The excretory system may always be filled by pricking 

 the body surface at any spot, though this method may give rise to 

 more or less extensive extravasation. The better plan is to introduce 



