PLATVHEEMINTHES 105 
about by the formation of many scolices from one proscolex. 
Thus, in Zaenia 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 Zaenia solium, which is common in man, has its 
bladder-worm, Cysticercus cellulosae, in the pig; it 1s, however, 
also found in man, and is the cause of considerable disturb- 
ance, often ending in the death of the host. Zaenia echinococeus, 
which is found in the sexual form in dogs, exists in the Cysti- 
cercus condition in man. 
The genus 7etrarhynchus is curiously modified, it appears 
to be flattened in a plane at right angles to that 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—Amphilina, found in Sturgeon. 
5. II. Caryophylaeidae—Caryophyllacus, found in intestine of Cyprinoid 
fishes, 
+ III. Pseudophyllidae—Bothriocephalus, Liqula, Archigetes, found in 
fishes. 
0 IV. Diphyllidae—Zchinobothriwm, found in Selachians. 
3 V. Tetrarhynchidae—Tetrarhynchus. 
55 VI. Tetraphyllidae—Anthobothrium, Calliobothrium, found in Sela- 
chians. 
» VII. Taeniidae—Zacnia. 
Cuass II]. TREMATODA. 
CHARACTERISTICS.—Platyhelminthes with a cylindrical or flat 
leaf-like body, devoid of segmentation. Their adhesive organs 
are tn the form of suckers. Hooks are rarely present. The 
excretory system ends internally in flame cells, and opens to 
the exterior by a contractile vesicle, or by two pores. They 
are parasite and hermaphrodite ; both 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. 
