144 ZOOLOGY 
pharynx is devoid of armature. They are hermaphrodite, 
and their reproductive organs are confined to a few segments. 
Their ova are laid in cocoons. Their developement is direct. 
The Oligochaeta were at one time divided into two 
groups: the Terricolae, which live chiefly on land, and the 
Limicolae, which are mostly aquatic. Recent research has, 
however, broken down the structural barriers which were 
believed to exist between the members of these two groups. 
The oligochaet worms are now arranged by Benham in a 
number of families, which allow themselves to be grouped in 
two divisions: (i.) the Naidomorpha, in which asexual repro- 
duction takes place; and (ii.) the Lumbricomorpha, in which it 
does not. The earthworm is the most familiar example of the 
latter subdivision. 
One of the most curious features found in many of the 
Oligochaets is the dorsal pore. In Lumbricus this pierces the 
skin on each segment in the middle dorsal line, and places the 
coelom directly in communication with the exterior. The pores 
occur in this genus on all the segments except the first six or 
seven. They are closed by a sphincter muscle, and opened by 
an anterior and posterior longitudinal band of muscles. They 
are found in several species of the Oligochaets,—Lumbricus, etc., 
—but do not occur in Polychaets.  Megascolides, a gigantic 
Australian worm, measuring from 4 to 6 feet in length, ejects 
through its dorsal pores the milky coelomic fluid with which 
it coats the walls of its burrows. 
The function of the modified skin of certain segments 
which constitutes the clitellum is to form the cocoons in 
which the eggs are deposited. It may completely enclose the 
body, and is then known as a cingulum, or it may be incom- 
plete. In the aquatic forms it only includes one segment : 
that on which the vas deferens opens. The capsulogenous 
glands also found in the skin give rise to the albuminous fluid 
found in the cocoon in which the ova and spermatozoa are 
deposited. This secretion serves to nourish the developing 
embryos. 
The septa which divide the body internally into segments 
are almost absent in Acolosoma; only one, dividing the head 
from the body, is present. 
