i64 ZOOLOGY FOR MEDICAL STUDENTS chap. 



front end joins the oviduct. At the point of junction the macrogametes 

 from the ovary meet the yolk-cells from the yolk-glands and they come 

 together into little packets, one gamete to a number of yolk-cells, each 

 enclosed in a horny-looking egg-shell ellipsoidal in shape and with a de- 

 tachable lid at one end (Fig. 74, A). The substance of the egg-shell is 

 generally believed to be secreted by the shell-gland (Fig. 76, s.g), a 

 spherical body with fuzzy surface which surrounds the point of junction 

 of yolk-duct and oviduct. 



From the shell-gland the female duct is continued onwards as a wide 

 winding tube, the uterus ( U), most of which is usually filled with eggs. 

 Towards its termination it becomes much narrowed and it opens to the 

 exterior at a point not quite half-way from the ventral sucker to the 

 mouth. 



The male organs are much less complicated than the female. The 

 testes (T), two in number, are greatly branched organs lying one in 

 front of the other, in the region of the body bounded in front by the 

 transverse yolk-duct and externally by the zone of yolk-glands. From 

 each testis there passes forwards a slender tube — the vas deferens (v.d), 

 that of the anterior testis lying on the left side. The two vasa deferentia 

 unite in the neighbourhood of the ventral sucker and form the expanded 

 seminal vesicle and this is continued onwards as a very fine tube, the 

 ejaculatory duct, which opens to the exterior close to the female opening. 

 The terminal part of the ejaculatory duct has thick muscular walls and 

 can be pushed out at the external opening forming the penis (p). 



The Liver-fluke has a very complicated and interesting life-history 

 (Fig. 74). The fertilized eggs (A) are laid within the bile-ducts, down 

 which they pass and eventually, after it may be accumulating for a time 

 in the gall-bladder, reach the intestine and so the exterior. Should the 

 egg fall on dry ground no further development takes place, but if it fall 

 into water there hatches out from it in the course of a few weeks — the 

 exact period varying with the temperature, being shorter in summer and 

 being prolonged by cold wintry weather — a larva of a characteristic kind 

 known as a miracidium (Fig. 74, B). The miracidium is a small creature 

 (about -12 mm. in length) looking to the naked eye as it swims about not 

 unlike a Paramecium. When examined under the microscope it is seen 

 to be in outline somewhat like the adult fluke. Its body is covered with 

 powerful cilia except just at the front end where there is a conical pro- 

 boscis (Fig. 74, B, p) which can be retracted and thrust out. A little 

 way behind the proboscis is a distinct nerve-ganglion (g) and embedded 

 in this a characteristic x-shaped eye. Further back in the body there 



