454 TEXT-BOOK OF ZOOLOGY 



The disease of the ears of wheat known among farmers as the 

 " purples " or "ear cockle " is due to a nematode parasite, the Wheat- 

 Eel (Tylenchus scandens), whilst another, the Thread-Worm of the 

 Turnip Disease (Heterodera schachti) has frequently caused great damage 

 among turnips. 



CLASS III.: FLAT-WORMS (PLATHELMINTHES). 



Body flattened, not divided into rings. 



ORDER I. : TAPE-WORMS (CESTODES). 

 The Human Tape- Worm {Taenia solium). 



A. Egg and Embryo, or Proscolex. 



The tape-worm, here to be considered, inhabits in its mature condition 

 the small intestine of man (name). Its eggs, which are of micro- 

 scopic minuteness, are discharged with the fseces (see Section C, 6). In 

 the interior of each egg is found already the rudiment of the future tape- 

 worm, viz., the embryo, or proscolex. It is surrounded by a thick resistant 

 capBule, and therefore not easily affected by moisture, heat, and cold. 

 In order that it may give rise to a tape-worm, it must find its way into 

 the stomach of a pig. Of this there is every probability, for this un- 

 clean animal is fond of burrowing among all kinds of filth, into which 

 eggs of tape-worms likewise easily find their way. In the stomach of the 

 pig, the capsule surrounding the proscolex is dissolved by the acid 

 gastric juices, and the latter set free. It works its way into the intestine, 

 the walls of which it pierces with its three pairs of movable hooks. 

 Thence it enters the circulation, and fixes itself within a muscle or other 

 organ. The hooks, being no longer required, disappear, and the proscolex 

 develops into a bladder-like vesicle, varying from the size of a pea to that 

 of a bean. In this condition it is known as — 



B. Cystic Worm, Cysticercus, or Scolex. 



From the wall of the vesicle projects into its cavity a hollow knob, or 

 invagination, at the bottom of which a wreath of small hooks and four 

 minute suckers (see cuttle-fish) may be distinguished even under a small 

 magnifying power (see Section C, 1). If the pig dies and is buried, the 

 scolices also perish. If, on the other hand, it is killed, and the flesh 

 eaten in an uncooked state by man, the scolices undergo their further 

 development to — 



