PLATYHELMINTHES 81 
The PLATYHELMINTHES are hermaphrodite ; in the female 
organs a vitellarium is often found. Reproduction may be 
asexual at times, and then an alternation of generations 
takes place. 
Cuass I. TURBELLARIA. 
CHARACTERISTICS. — Free - living Platyhelminthes, whose ovat, 
usually flattened body is covered with cilia. A mouth, a 
muscular pharynx, and an alimentary canal exist, but no 
anus. No special respiratory system or vascular system, or 
hooks, are present. Nervous system, a paired cerebral 
ganglion and two lateral nerve cords. With few exceptions 
hermaphrodite. 
The Turbellaria are mostly aquatic, inhabiting the sea 
and fresh water, but a few live on the earth amongst damp 
Fic. 55.—Various forms of Turbellaria, 
all natural size, and viewed from the 
dorsal surface. After Von Graff. 
4. Convoluta paradoxa, Oe. 
Vortex viridis, M. Sch. 
. Monotus fuscus, Gff. 
d. Thysanozoon brocchii, Gr., with ele- 
vated anterior extremity (after 
Joh. Schmidt). 
Rhyncodemus terrestris, O. F. Miiller 
(after Kennel). 
Jf. Bipalium ceres, Mos. (after Moseley). 
oS 8 
is) 
SS 
. Polycelis cornuta, O. Sch., attached 
by the pharynx (ph) to a dead 
worm (after Johnson). 
Ss 
surroundings (Fig. 55); a very few are parasitic, and then 
occur in Mollusca or Holothurians. Several are common in 
ditches and standing water in England; Planaria lactea, a 
Dendrocoel, especially so. One of the Rhabdocoela, which 
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