EARTHWORM. 213 
surface there are not a few special apertures, which should be looked 
for on a full-grown worm ; but careful examination of several specimens 
is usually necessary. Almost always plain on the 15th ring are the 
two swollen lips of the male ducts, 
less distinct on the 14th are the 
apertures of the oviducts through 
which the eggs pass, while on each 
side, between segments 9 and Io, 
1o and 1r, are the openings of two 
receptacula seminis or spermathecze 
into which male elements from 
another earthworm pass, and from 
which they again pass out to fertilise 
the eggs of the earthworm when 
these are laid. Each segment 
contains a pair of excretory tubes, 
which have minute ventral-lateral 
apertures, while on the middle line 
of the back, between the rings, 
there are minute pores, through 
which fluid from the body cavity 
may exude on to the skin. 
Fic. 111.—Anterior region of 
earthworm,—After Hering. 
Skin and bristles. — The ee the eight setze (s.) on each segment. 
. : : S., Spots between g-10, 10-11, 
thin cuticle is produced by indicate openings of receptacula 
the cells which lie beneath, Siti nd openings of oviduct 
and is perforated by the aper- _deferentia on segment x, 
tures previously mentioned. 
The epidermis clothing the worm is a single layer of cells, 
of which most are simply supporting or covering elements, 
while many are slightly modified, as glandular or mucous 
cells, and as nervous cells. As the latter are connected 
with afferent fibres which enter the nerve-cord, the skin is 
diffusely sensitive. In a few species the skin is slightly 
phosphorescent. The chitinous bristles, which are longest 
on the genital segments, are much curved, and lie in small 
sacs of the skin, in which they can be replaced after 
breakage. 
Muscular system and body cavity. — The earthworm 
moves by the contraction of muscle cells, which are 
arranged in circular hoops and longitudinal bands under- 
neath the skin. The special muscles above the mouth 
and pharynx have considerable powers of grasping, while 
less obvious muscular elements occur in the wall of the 
gut, in the partitions which run internally between the 
