122 INVERTEBRATE ANIMALS. 
lanceotatum (fig. 51, 2) the intestine is divided into two branches, 
but these are simple tubes, and are not branched. 
ORDER III. TurBELLARIA.—The animals included in this 
order differ altogether from the Zyvematoda and Teniada in 
being almost all aquatic in their habits and being all non-para- 
sitic. ‘They never possess sucking-discs or hooklets, and their 
integument is always furnished with vibrating cilia. A water- 
vascular system is always present, but it appears sometimes not 
to communicate with the exterior. The alimentary canal is 
sometimes simply hollowed out of the tissues and destitute of 
an anus, as in the 7yemafoda, and at other times suspended in 
a free space (body-cavity) and furnished with an anus. It may 
‘be simple or much branched. 
The best known of the members of this order are certain 
little, jelly-like, soft-bodied, ovate, or elliptical creatures, which 
are commonly found in fresh water,or on the sea-shore, and are 
known as Planarians. The skin in these curious little animals 
on 
Fig. 52.—Turbellaria. 1. Planaria torva: m Mouth; g Nerve-ganglion; e Eyes; 
ov Ovary; ¢Spermarium; g# Genital opening: 2. Planxaria lactea, showing 
the branched intestine: 3. Larva of one of the marine Turbellarians: 4. P7d- 
zdium, the larva of one of the Nemertide, 
(fig. 52, I, 2) is richly furnished with cilia, and also contains 
numerous cells which have been compared to the “ nettle-cells” 
or “cnide” of the Cwlenterata. The intestine may be either 
straight or branched, but always terminates behind in blind 
pouches, and is never provided with an anus. The water-vas- 
cular system communicates with the exterior. The nervous 
system consists of two ganglia, placed in front of the mouth, 
