

8 II. —CHARACTERS AND STRUCTURE OF THE LEPIDOPTERA. 
CHAPTER 
I]. 
ON THE GENERAL CHARACTERS AND STRUCTURE 
OF THE LEPIDOPTERA.* | 
Butterflies and moths together form one of the great 
orders of insects termed Lepidoptera (from the two Greek 
words Aeris a_ scale, wing), of which 
the most striking character is that the wings are clothed 
with scales. The mouth of these insects is suctorial, the 
maxille forming a spiral proboscis which is coiled up 
between the large labial palpi when not in use (see Plate 
B, figs. 5 and 6). The other oral organs are rudimentary. 
To acquire this form these insects pass through three very 
distinet stages, viz., the Egg, the Larva, and the Pupa. 
The eggs of Lepidoptera are generally somewhat globu- 
Jar, much flattened above and beneath. (See frontispicee.) 
Some are very elaborately sculptured, whilst others are 
quite smooth. They are’ usually white, yellowish, pale 
green, or pale blue, but always change much in colour as 
the contained embryo develops. In most eggs there is a de- 
pression, often in the form of a rosette, from which the 
sculptured ribs, or rows of hexagonal depressions radiate. 
This depression is called the micropyle, and it is through 
an opening here situated that the spermatozoa gain access 
to the germ during the process of fertilization. Some eggs 
are laid with the axis terminated by the micropyle in a 
vertical position, and these are described as upright; others 
with the micropylar axis horizontal, and to these the term 
flat is applied. 
and mrepov a 
The larve of butterflies and 
known as eaterpillars. 
moths are popularly 
They usually consist of thirteen 
clearly-defined segments, segment number one being the 
head. The head is furnished with several simple eyes 
(Plate B., fig. 2, AA), a pair of very short antennze (BB), 
and a very powerful masticatory mouth. The mouth con- 
sists of the following organs: The labrum, or upper lip (i 
a pair of mandibles, or upper jaws, working like scissor- 
blades (2, 2); two maxille, or lower jaws (3, 3), each 
carrying a jointed organ termed the maxillary palpus; and 
the labium, or lower lip (4); which bears another pair of 
minute jointed appendages—the labial palpi. 
Segments 2, 3, and 4, which answer to the thorax of 
the perfect insect, are each furnished with a pair of legs. 
They consist of the six following joints (fig. 2): (@) coxa, 
(b) trochanter, (c) femur, (d) tibia, (e) tarsus, and (f) 

“In this chapter only the briefest possible summary is 
given of the general characters and structure of the Lepidop- 
tera. Those who desire more detailed infermation will, of 
course, consult some of the numerous text books, now ayail- 
able, on the morphology of the Lepidoptera and other insects. 
claw. These legs correspond to those of the perfect insect. 
The remaining nine segments of the body constitute the 
abdomen. Usually segments 7 to 10 and 13, each have a 
pair of fleshy pads, which are termed prolegs and are fur- 
nished on their edges with a row of minute hooklets (see 
Plate B., fig. 14, proleg highly magnified). It is these 
hooklets which enable caterpillars to hold on by means of 
their prolegs with such great tenacity. The number of the 
prolegs varies considerably in different families. The 
spiracles, or orifices of the air-tubes, are situated on each 
side of the larve just above the legs. With the exception 
of the head and segments 3, 4, and 13 there is a pair of 
spiracles on each segment. The larva is provided with a 
very complete digestive system, which consists of the fol- 
lowing organs (see Plate B., fig. 9); A, the esophagus; D, 
the ventriculus; F, the clavate intestine; E, the ilium; H, 
the colon; K, the malpighian tubes; and O, the spinning 
vessels. These last open at a small orifice in the labium 
termed the spinneret (fig. 2,5). They supply the silken 
threads which are employed by most larve in constructing 
their cocoons, and which also serve in cases of danger as a 
rapid means of retreat. In describing the markings on a 
larva, we distinguish the line down the mid-back as the 
dorsal line, and those on each side of it as swb-dorsal lines; 
the line near the spiracles is termed the lateral or spiracular 
line, and any other markings present are referred to in 
connection with their proximity to these lines.. 
The entire growth of the insect is accomplished during 
the larval condition, the increase in size being frequently 
very rapid. Owing to this cireumstance larve are often 
compelled to shed their skin, and in many species a very 
considerable alteration both in the shape and colour takes 
place at each moult, or ecdysis as it is sometimes termed. 
The period between each successive moult is termed an 
instar; the first instar being the stage immediately follow- 
ing the egg, the second instar that following the first moult, 
and so on, 
The pupa of a Lepidopterous insect is completely 
encased in a chitinous envelope. With the exception of a 
slight twirling of the abdominal segments it is incapable of 
any motion. In the pupa of Micropteryx and its allies the 
mandibles and labial palpi are functionally active, but this 
is a very exceptional though extremely interesting case. 
The number of free or movable segments of pupz varies 
considerably in different families and genera, and by some 
authors it is regarded as a character of much importance in 

