PLATYHELMINTHES 105 



about by the formation of many scolices from one proscolex. 

 Thus, in Taenia coenurus, the bladder-worm which gives rise 

 to the " staggers '' in sheep produces several heads, and thus 

 several scolices are produced asexually, which in their turn, 

 if they attain their right host, reproduce sexually. 



The Taenia solium, which is common in man, has its 

 bladder- worm, Cysticercus cellulosae, in the pig ; it is, however 

 also found in man, and is the cause of considerable disturb- 

 ance, often ending in the death of the host. Taenia echinoco'ccus, 

 which is found in the sexual form in dogs, exists in the Cysti- 

 cercus condition in man. 



The genus Tetrarhynchus is curiously modified, it appears 

 to be flattened in a plane at right angles to th^t of other 

 Cestoda. The head bears four long hooked proboscides, which 

 can be protruded from two disks ; each of the latter seems to 

 be homologous with two of the suckers of Taenia. 



The Cestoda are divided into seven families : 



Family I. Amphilinidae — AmpMliTux,, found in Sturgeon. 



„ II. Caryophyllaeidae — Caryophyllaeus, found in intestine of Cyprinoid 



fishes. 



,, III. Pseudophyllidae — Bolhriocephalus, Ligula, Arckigetes, found in 



fishes. 



, , IV. Diphyllidae — EcMnobothriii/m, found in Selachians. 



,, V. Tetrarhynchidae — Tetrarhynchus. 



,, VI. Tetraphyllidae — Anfhobothrium, Calliobothriwni, found in Sela- 

 chians. 



„ VII. Taeniidae — Taenia. 



Class III. TREMATODA. 



Characteristics. — Platyhelminthes with a cylindrical or fiat 

 leaf -like hody, devoid of segmentation. Their adhesive organs 

 are in the form of suckers. Hooks are rarely present. The 

 excretory system ends internally in flame cells, and opens to 

 the exterior hy a contractile vesicle, or hy two pores. They 

 are parasitic and hermaphrodite ; hoth reciprocal and self- 

 fertilisation occur. The embryo may develop directly, or it 

 may pass through a series of stages, in some of which asexual 

 reproduction takes place. 



Fasciola (Distoma) hepatica, commonly known as the 

 liver fluke, is found in the liver of diseased sheep. It is 

 about |- of an inch long, and has a flattened leaf-like shape. 



