302 Turbelt.aria. TURBELLARIA. Teretulakia. 
Class — TURBELLARIA (The Planarias, Nemertines, &c.) 
This class of worms was established by Ebrenberg, 
and has been revised by Oersted. It contains, accord- 
ing to the arrangement of Dr. Johnston, all these non- 
parasitical worms the body of which is not divided 
into segments, and which is destitute of bristles on the 
sides, described in the previous class of Annelides as 
taking the place of feet. The extremities of the body 
are simple, and continuous with it, there being no dis- 
tinct head visible. In form this body is either flat or 
subcylindrical ; in substance soft, parenchymatous, or 
cavernous, and in general it is naked and lubricous. 
The whole body is covered more or less with vibratile 
cilia or with papillae ; it is often very contractile, 
assuming a variety of shapes at diflei’ent times, and 
there are some species which break up voluntarily into 
pieces. The front portion of the body, the head being 
imperfectly defined or completely continuous with the 
body, has in most cases no tentacula, but in some 
genera there are two, prolonged from the surface. 
The mouth in some is terminal, in others ventral ; and 
in the latter case it is situated in the anterior third, 
or near the centre, or towards the tail, and is often 
furnished with a protrusile proboscis. The intestine in 
one group runs undivided through the length of the 
bod}', and in another is dendritically branched ; and in 
these latter this canal is without a vent. The Turbel- 
laria are either of separate sexes, or they are herma- 
phrodite; most of them propagate by ova, but some 
by transverse fissuration. These worms are animal- 
feeders for the most part, though there are some which 
appear to make their diet, in part at least, consist of 
decaying vegetable n)atters. In general they are 
natives of salt or fresh water, though a few are found 
on land in moist places. Their mode of progression 
is by gliding smoothly along the surface of any body 
upon which they attach themselves, as under stones, on 
the leaves of algae and submerged plants, &c., or b}' 
swimming, an act which they execute rather slowly. 
A few of the species are found taking up their abode 
in the deserted tubes of other worms, or even, though 
rarely, forming for themselves a sheatU of dried gluten 
of considerable tenacity. 
The class Turbellaria may he divided into two 
orders — I. Planaria, containing the true Planarias ; 
and 11. Teretularia, containing those long linear or 
riband-shaped worms, called Linens, Borlasia, or Ne- 
mertes, &c. 
Order I. — PLANARIA {The Planarias). 
The body of these worms, as their name would 
indicate, is flattened, and usually not much longer than 
broad. It is covered with a ciliated epithelium, and is 
of a loose, cellular, parenchymatous structure. A few 
are destitute of eyes, but the greater number have them 
pretty well developed, and sometimes even numerous 
and arranged in clusters. The mouth is a simple pore, 
and often furnished with a protrusile proboscis. The 
intestine has no vent or posterior opening, and is either 
in form of an undivided tube, or branched like a 
shrub. 
This latter character has been taken as a means of 
dividing the order into two sub-orders or large groups 
— Rhuhdoccela, and Dendrocmla. 
Sub-order I. — EHABDOCH5LA. 
Alimentary canal simple and cylindrical ; no pro- 
trusile proboscis ; locomotion mostly natatory. 
The animals of this group are small, aquatic crea- 
tures, living both in fresh water and salt. The body 
is of a parenchymatous consistency, and it is -often 
difflcult to trace any distinctly-defined viscera or their 
openings. It is contractile to a certain extent, and has 
an entire margin. There is no distinct head, and in 
some the eyes are altogether wanting, whilst in others 
they occur only two in number. The mouth is either 
terminal or nearly so. The fresh-water species pro- 
pagate by ova, and these are laid inclosed in a cocoon 
or capsule. The marine species are less known. A 
good many species are found in this country ; and one 
genus has been named Dalyellia, in compliment to 
Sir John Dalyell, the author of a very interesting account 
of British Planaria. 
Sub-order II. — DENDROCHilLA. 
Intestinal canal dendritically ramified; a protractile 
proboscis ; locomotion reptatory. 
Fig. 206 
Planaria maculata. 
This sub -order contains many more species than the 
preceding, and to it belong the true Planarias. The 
accompanying figure will represent the order Pla- 
naria. — See fig. 206. 
Order II. — TERETULARIA {The Nemertines). 
The worms of this order have a body linear in shape, 
and very much (in some cases nearly a thousand times) 
longer than broad. It is soft and glutinous, very often 
covered with vibrating cilia, and so contractile, that 
when extended in the act of moving through the water 
or mud. they exceed their length when at rest by three 
