106: NEW ZEALAND NATURE-STUDY BOOK 
through the skin—as frogs do when under water. It is 
for this reason that Worms are nocturnal in their habits, 
and quickly die if exposed to a strong sun. The hot sun 
dries up the moisture on the skin and so the air is unable’ 
to, pass through and supply the blood with oxygen. 
Locomotion. The rings of which the body is com- 
posed can be compressed and lengthened, or widened 
and shortened by means of special muscles. This has the 
effect of elongating or shortening the body, and so of 
enabling the animal to crawl along. Its power of loco- 
motion is greatly assisted by short bristles carried by the 
segments. The bristles are directed backward, and as the 
body is elongated they move over the ground without 
catching, but firmly fix the fore part when the body begins 
to contract, the net result being a forward movement. 
On all the segments except those in front, there are four 
pairs of these bristles (setae), two pairs on _ the under 
surface, and one pair at either side, 
Burrowing. Worms burrow in the soil, the shape of 
the body being specially fitted for this purpose. When 
about to burrow the worm elongates the fore part of its. 
body which becomes thin and pointed. It then feels 
about until it finds a crevice in the soil into which it 
thrusts the pointed head. The operation of dragging 
itself into the burrow causes the body to shorten and 
thicken and so widens the opening. If the soil be too 
compact to burrow in, the animal gnaws its way along 
swallowing the earth, most of which passes through its 
body and is delivered at the surface in the form of 
worm-castings. ‘The mucus poured out on the skin, by 
making it slimy and hence reducing friction, enables the 
animal to move through the soil with much greater ease, 
Senses. ‘The Worm is without the sense of hearing, 
and has but little sense of sight. Its sense of 
