FLUKES 247 



conspicuous organ. The vitellaria are bilateral branching glands which pour 

 nutrient material into the ootype. It is in the ootype that the eggs are formed, 

 and opening into it we have the adjacent ovary. The shell gland is near the ovary. 



A canal, known as Laurer's canal, leads from the ootype to the exterior, the 

 function of which is in question. It is probable that as trematodes have no sperma- 

 theca, the spermatozoa from other flukes enter by way of this canal. The life his- 

 tory of the important human flukes is unknown. It is supposed that this, in a meas- 

 ure, may resemble that of the common liver-fluke of sheep (sheep rot). In this the 

 eggs containing a ciliated embryo (miracidium) pass out in the faeces. This embryo 

 is hatched out and, gaining the water, swims about actively until it reaches some 

 suitable mollusk (Limnaea truncatula). By means of a pointed end, it bores its 

 way into the body of the gasteropod and in the pulmonary chamber becomes a 

 bag-like structure (the sporocyst) from the germinal cells of which develop a creature 

 with an alimentary canal (redia). The rediae tend to break out of the sporocyst and 

 wander to the liver of the snail. These rediae may give rise to a second generation 

 of rediae. 



From the rediae minute little worms resembling adult flukes in possessing suckers, 

 but differing in the possession of a tail, develop (cercaria). Having reached maturity, 

 these cercariae leave the rediae, and, as in case of Fasciola hepatica, lose the tail, be- 

 come encysted on blades of grass, to be eaten by sheep and again commence the cycle. 

 The encysted cercariae develop into adult liver flukes. It is probable that with many 

 flukes the cercarise enter some host, as mollusk, insect, or fish, and that it is by eat- 

 ing such animals as food that man becomes infected. Looss thinks it possible that 

 the miracidium of Schistosomum haematobium may bore its way directly into man, 

 as do the larvae of the hookworm. Manson also suggests that the reporting by Mus- 

 grave of 100 mature lung flukes in a psoas abscess makes it very probable that these 

 parasites entered the body as miracidia. The idea in China is that the infection 

 with the common liver fluke of man is brought about by eating fish. Fluke disease 

 is generally known as distomatosis or distomiasis. 



LIVER FLUKES. 



Fasciola hepatica (Distomum hepaticum). This fluke, while of 

 enormous economic importance by reason of destruction of sheep, has 

 only been reported twenty-three times in man, and in these instances 

 does not seem to have occasioned marked symptoms. 



It has a cone-shaped anterior projection and is about 11/4 inch (30 mm.) long. 

 The intestinal canal, as well as the testicles, is branched. There is, however, a possible 

 importance of F. hepatica in connection with a peculiar affection known as "halzoun. " 

 This results from the eating of raw goat-liver, and it is supposed that the flukes 

 crawl up from the stomach and, entering the larynx or attaching themselves about 

 the glottis, produce the asphyxia characteristic of the disease. 



Dicrocoslium lanceatum. This has only been reported seven times in man. 

 The symptoms are unimportant. The fluke is about 1/3 of an inch (8 mm.) long, 

 with testicles anterior to the uterus. 



