8 BUTTERFLIES AND MOTHS. 
are called abdominal segments, and these form later the 
abdomen of the adult orimago. The abdominal segments 
carry the false legs or prolegs, which disappear in the butter- 
fliesormoths. Such prolegs are not jointed but are equipped 
with rings of hooks that enable the caterpillar to grasp se- 
curely the object on which it moves; the last segment is 
usually distinguished by a pair of prolegs formed somewhat 
differently from the others. Most caterpillars possess, in- 
cluding the true legs, sixteen legs, but the loopers or meas- 
uring worms have only ten, aiid those living in bags but six. 
All caterpillars, or worms looking like caterpillars, which 
possess more than sixteen legs, are not the larve of lepidop- 
tera, but are those of saw-flies, insects belonging to the 
order of Hymenoptera. Such worms are called ‘‘ false cater- 
pillars.’”’ Upon the first thoracic segment of a true cater- 
pillar we find quite often a horny plate; this is the cervical 
shield, used in throwing off the head-plate when the insect is 
Fig. 12.—Moultingof the caterpillar of Danais archippus; a, larva suspended; 
b, pupa still partly in larval skin; c, pupain the act of leaving the skin entirely. 
After Riley. 
moulting; another plate, the anal-shield, occurs frequently 
upon the last segment. The breathing-pores or stigmata 
occur as small openings upon the sides of the body. Notall . 
caterpillars are cylindrical, however, and forms occur that 
resemble in external shape sow-bugs or slugs. Some cater- 
pillars are densely covered with hairs, sometimes arranged 
in tufts or brushes; others are only clothed with a few 
hairs, or with spines, while still others are naked. 
