196 UNSEGMENTED “WORMS.” 
Tetraphyllidee. With four very mobile suckers. 
e.g. Echeneibothrium, Phyllobothrium. 
Teeniide. With four suckers, often with apical hooks, with marginal 
genital apertures. 
eg. Tenia. 
GENERAL NOTE on Ptaty- 
HELMINTHES 
The four classes Turbellaria, 
Trematoda, Cestoda, and Temno- 
cephaloidea, constitute the Platy- 
helminthes or  Flat-worms — an 
interesting group, because its mem- 
bers illustrate so well the progressive 
degeneration associated with increas- 
ing parasitism, and also because of 
the relatively great simplicity. The 
four classes are nearly related, for 
forms like Zemmnocephala connect 
Turbellaria and Trematoda, and the 
H “‘monozoic” Cestodes like <Archd- 
getes, Amphilina, Caryophylleus, 
and Gyrocotyle connect Trematoda 
sit and Cestoda. It is probable that 
both Cestodes and Trematodes arose 
from a Turbellarian stock. 
Among the most striking of the 
Platyhelminth characters are the 
nature of the excretory and repro- 
ductive organs and the condition of 
the mesoderm. The excretory system, 
with its longitudinal trunks, its 
ramifying canals, and ‘‘flame-cells,” 
is characteristic. The reproductive 
organs are complex, show division 
Fic. 102.—Diagrams of of labour, and are furnished with 
bladder-worms. ducts of their own, unconnected with 
L. The ordinary Cysticercus type the excretory system—a condition 
with one head (/.). not common elsewhere. The pres- 
Il. The Cente type, with many ence of shells around the eggs is 
eads. | = S 
igh Bie eiieokeeens ened) with another point of interest. It be 
many heads, and with’ brood comes of great importance to the 
capsules producing many parasitic flukes and tape-worms, but 
heads. occurs also in the free - living 
‘ Turbellaria. The formation of yolk 
cells from a specialised part of the ovary (yolk gland) is also note- 
worthy. There is no true body-cavity, the space between gut and 
body-wall being filled with a packing tissue; the absence of an anus 
is also important, the two characters taken together being held to 
indicate affinity with the Ctenophora. 
