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THE ELEMENTS

OF

INSECT ANATOMY

AN OUTLINE FOR THE USE OF STUDENTS
IN ENTOMOLOGICAL LABORATORIES

BY

JOHN HENRY COMSTOCK

PROFESSOR OF ENTOMOLOGY AND GENERAL INVERTEBRATE ZOOLOGY
IN CORNELL UNIVERSITY

AND

VERNON L. KELLOGG

PROFESSOR OF ENTOMOLOGY IN LELAND STANFORD, JR., UNIVERSITY

SEVENTH EDITION, REVISED

ITHACA, NEW YORK

COMSTOCK PUBLISHING CO.

1910

COPYRIGHT, 1899, BY
JOHN HENRY COMSTOCK

PREFACE

The course of study outlined in the following pages is de-
signed to enable students to learn the more general features
of the structure of insects. It may serve as an introduction
to a more extended study of insect morphology.

While the more obvious object of this course is the learn-
ing of certain facts, a much more important thing to be
gained is a training in methods of careful observation. The
student is urged, therefore, to do the work with great care.

CONTENTS

CHAPTEK PAGE

1. TERMS DENOTING POSITION AND DIRECTION OF

PARTS i

II. THE EXTERNAL ANATOMY OF A LOCUST, Mdanoplus

femur-rubrum 7

III. THE INTERNAL ANATOMY OF AN INSECT, Corydalis

cor nut a , . tf . . 31

IV. THE ANATOMY OF THE LARVA OF THE GIANT CRANE-

FLY, Holorusiii rubiglnosa ... 54

V. THE EXTERNAL ANATOMY OF A BEETLE, Pterostichus

californicus 63

VI. THE MOUTH-PARTS OF INSECTS 74

VII. THE VENATION OF THE WINGS OF INSECTS 86

VIII. METHODS OF INSECT HISTOLOGY 121

INDEX AND GLOSSARY 140

CHAPTER I.

TERMS DENOTING POSITION AND DIRECTION OF PARTS.

Need of a technical nomenclature. — It has been found
that the use of the terms upper, lower, inner, outer, before,
behind, anterior, posterior, and similar expressions in the
technical descriptions of animals or their parts frequently
leads to ambiguity. A great part of the confusion doubtless
arises from the fact that the natural position of man differs
from that of the lower animals in being erect. Thus, for ex-
ample, when applied to men, before means in the direction
indicated by a line drawn from the center of the body to the
ventral surface ; in the lower animals it means in the direc-
tion indicated by a line drawn from the center of the body to
the head. The same difficulty attends the use of the term
anterior ; and of the opposite of these terms, behind and
posterior.

Another source of confusion in the use of this class of
terms is the fact that they are very commonly applied with
reference to the plane of the horizon. Thus above means
towards the zenith ; below, towards the nadir ; and before and
behind indicate directions parallel to the plane of the horizon.
Consequently whenever the position of an object is changed
the terms denoting the relation of its parts must be changed.

In order to avoid these difficulties a special set of terms
for designating the position and direction of the parts of
animals has been adopted by many writers ; and it is the
object of this chapter to define such of these terms as are
used in this book.

Construction of the terms used. — Excepting the noun
meson, the terms used in this work for denoting the position
and direction of parts are either adjectives or adverbs.

The adjectives end in al, as dorsal, ventral, and mesal ;
the adjectives cephalic and intermediate are exceptions to
this rule.

The adverbs are formed by substituting for the adjective
ending the ending ad, the Latin equivalent of the English
suffix ward. Thus from the adjectives dorsal, ventral, and
mesal, are formed the adverbs dorsad, ventrad, and mesad.

In forming compound words indicating position or direc-
tion, the vowel o is substituted for the termination of the first
member of the compound, as dorso-ventral, caudo-cephalic.

The six cardinal directions. — There are six principal
directions to which the position and direction of the parts of
a bilaterallv symmetrical animal, like an insect, are com-

* *

monly referred ; these are as follows :

The cephalic direction or headward ; this is the direction in-
dicated by a line drawn from the center of the animal to the
head.

The caudal direction or tailward ; this is the opposite of the
cephalic direction.

Two lateral directions, or towards the right and towards the
left.

The ventral direction or bellyward ; this is the direction
indicated by a line drawn from the center of the body to the
ventral surface and forming a right angle with each of the
preceding directions.

The dorsal direction or backward ; this is the opposite of
the ventral direction.

The adverbial forms of the adjectives cephalic, caudal.
lateral, ventral and dorsal are cephalad, caudad. laferad. -centra.:.
and dorsad. Thus a part which extends in a cephalic direc-
tion may be said to extend cephalad.

It should be carefully noted that cephalad does not neces-
sarily mean towards the head but headicard ; that is, to-
wards a point which is in a direction indicated by a line
drawn from the center of the animal to the head, but at an
infinite distance in that direction. In other words, these terms
must be used in a way analogous to that in which we use
right and left.

EXAMPLE. — Take a figure of a Dragon-fly with its wings extended as
when at rest. Draw a line from the distal extremity of one of the wings
to the head. Although this line extends directly towards the head it does
not extend cephalad; but more or less nearly mesad.* A line extending
cephalad from the distal extremity of a wing (or from any other part) is
parallel to the cephalo-caudal axis of the body.

Differences between the technical and popular uses
of cephalic and caudal. — It has just been shown that in
the use of these terms it is not the head and tail to which
the position and direction of parts are referred, but to two
of the cardinal directions which are at right angles to
right and left. Thus we can speak of the caudal part
of the head or of the cephalic portion of the tail. It will
be seen that this does not accord with the popular uses
of these terms (as defined in the dictionaries) according to
which no part of the body is cephalic except the head ; and
of the different parts of the head one is just as much cephal-
ic as another.

Oblique lines. — The position or direction of a part
towards a point between two of the cardinal points can be
designated by a compound term.

EXAMPLE. — A part which extends in a direction between those direc-
tions which are indicated by dextrad and caudad is said to extend dextro-
candad.

Meson, mesal, and mesad. — Frequently the position
or direction of a part is referred to an imaginary plane di-

' Mesad is defined later.

viding the body into approximately equal right and left
halves. This middle plane is called the meson (/xeo-o^, mid-
dle). From meson are derived the adjective mesal and the
adverb mesad.

Ectal, ectad, ental, and entad. — It is often necessary,
especially in the study of internal anatomy, to compare parts
with relation to their nearness to or remoteness from the
surface of the body. For this purpose the terms ectal (CKTOS,
without) and ental (eVros, within) are used. The adverbial
forms of these terms are ectad and entad.

EXAMPLE. — The principal muscles of an insect are attached to the ental
surface of the body-wall, or to parts of the body-wall which project entad.
The hairs or spines on the body-wall project ectad.

Aspects of the body.— In describing animals it is often
desirable to specify that part of the body which looks in a
certain direction. For this purpose the term aspect is used
combined with an adjective indicating the direction in which
the surface in question looks.

EXAMPLES. — Dorsal aspect, ventral aspect.

Six aspects of the body are recognized ; these are dorsal,
ventral, cephalic, caudal and the two lateral. The fact
that the outlines of the body of an animal are more or less
curved does not interfere with the practical application of
the above terms.*

Proximal, distal, proximad, and distad. — In describ-
ing appendages of the body (legs, wings, etc.) the position of
parts may be referred to the two ends of the appendage by
use of the terms proximal and distal. Proximal indicates
nearness to the end of the appendage which is attached to
the body ; distal, to the end which is free. From these ad-

* Cases occur where it is desirable to speak of an aspect which looks in a
direction between two of the cardinal directions. Thus we speak ot the lines or
spots on the latero-dorsal aspect of a larva.

5

jectives the adverbs proximad (towards the proximal end)
and distad (towards the distal end) are formed.

EXAMPLES. — The proximal segment of the leg of an insect is the coxa.
The segments of the leg distad of the tibia constitute the tarsus.

Aspects of appendages. — In addition to the two ends
of an appendage four aspects are recognized. To these the
same terms are applied as to the corresponding aspects of
the body : viz.y dorsal, ventral, cephalic, and caudal. It is
therefore necessary to have a rule by which the correspond-
ence between the aspects of the body and of appendages can
be determined. In other words, a definite position must be
chosen as the normal position of an appendage. Naturalists
are quite well agreed as to what is the normal position of
the limbs of the Vertebrates. The following are what we
believe to be the analogous positions for the legs and wings
of insects.*

(<?.) Wings. — Extended horizontally at right angles to the
body as are the wings of a dragon-fly (Libellula) when at
rest.

(/'.) Legs. — Extended horizontally at right angles to the
body so that the convexity of the articulation between the
two principal segments of the leg (femur and tibia) shall look
dorsad ; and so that the surface of the tarsus (" foot") which
is usually applied to the ground when walking shall look
ventrad.

The dorsal, ventral, cephalic, or caudal aspect of a wing or
leg is that aspect which, when the wing or leg is in its normal
position, looks in the same direction as does the aspect of
the body which bears the same name.

First, second, third, etc. — When the members of a
series of parts forming a portion or the whole of the trunk

* The necessity for referring to the aspects of other appendages than the legs
and wings will so seldom arise that it does not seem worth while to attempt to
determine the normal positions of such appendages.

are indicated by the terms, first, second, third, etc., the
cephalic member of the series is the first.

EXAMPLE. — Theyf^j/ abdominal segment is the one nearest the head.

When the series forms a part or the whole of an append-
age of the body, the first member of that series is the proxi-
mal one.

EXAMPLE. — The first segment of a leg is the one which is articulated to
the body.

The direction of an appendage does not modify the above
rule.

EXAMPLE. — The first segment of an antenna is the one which is articu-
lated with the head ; notwithstanding that when the antennas are directed
cephalad, as is usually the case, this segment is the one nearest the caudal
end of the body.

Intermediate. — In order to avoid ambiguity the word
mesal and its derivatives are used only with reference to the
meson. The second member of a series of three similar parts
is designated as the intermediate one.

Limitations to accuracy. — As the body of an animal
presents but few plane surfaces or straight lines it is often
impossible to describe the position or direction of a part with
absolute accuracy> Practically, however, one will meet with
but few serious difficulties. Thus in describing the direction
of a curved or undulating line on the surface of the body it
will rarely be necessary to do more than to give the general
direction of that line ; the reader will understand that it fol-
lows the sinuosities of the surface of the body.

CHAPTER II.

THE EXTERNAL ANATOMY OF A LOCUST.
(Melanoplus femur-rubntm, )

Locusts or short-horned grasshoppers are excellent
subjects to use in beginning the study of the external anat-
omy of insects. They are very common and are compara-
tively large ; and the parts of the external skeleton in these
insects are mostly remarkably distinct.

The species which has been selected as the basis of this
outline is the red-legged locust, Melanoplus femur-rubrum,
which is found in nearly all parts of the United States.
Specimens of this insect, preserved in alcohol, will be fur-
nished the student, who will be expected to verify carefully
or to correct each statement made in the text.

In order to illustrate certain points not well shown in the
locust, comparative studies will be made of parts of a cock-
roach.

DIVISION OF THE BODY INTO REGIONS.

The body of a locust is composed of a series of more or
less ring-like segments. In the caudal part of the body the
ring-like nature of the segments is obvious ; in the cephalic
part it is less so. These segments are grouped into three
regions : head, thorax, and abdomen.

Head. — The head is the first or cephalic of the three
regions of the body. Apparently it consists of a single seg-
ment.

8

Thorax. — The thorax is the second or intermediate region
of the body. It is readily distinguished by its appendages ;
which are three pairs of legs and two pairs of wings. It
consists of three segments ; but as each segment is com-
posed of several distinct pieces, it requires considerable
study to trace the outlines of each segment. We will return
to this subject later.

Abdomen. — The abdomen is the third or caudal region
of the body. The segments of which it is composed are
more simple, distinct, and ring-like than those of the other
regions.

STRUCTURE OF THE BODY-WALL.

Chitin.— In studying the anatomy of insects it is found
that in the adult stage the greater portion of the body-wall,
that part of the insect which corresponds in position to the
skin of higher animals, is hard.

This hardness is due to the deposition of a horny sub-
stance, called chitin, in the membrane which constitutes the
body-wall.

Sclerites. — The chitin is not evenly distributed through-
out this membrane. Pull the head of a locust so as to sepa-
rate it from the thorax as far as possible without breaking
the skin. Note that the head is joined to the thorax by a
soft flexible membrane, in which but little, if any, chitin
has been deposited.

Examine the sides of the thorax with a lens and observe
that the body-wall appears to be made up of many distinct
pieces. The integument is, however, really continuous ; and
in each case what appears as a distinct piece is simply a por-
tion of the body-wall in which considerable chitin has been de-
posited. Such a portion of the body-wall is called a sderite*

* The sclerites are analogous to the centers of ossification in the bones of the
higher animals.

Sutures.— The sclerites constitute the greater part of the
body-wall, the soft membranous portions separating them
being in most cases narrow. Usually these narrow portions
are mere lines; they are then called sutures.

Frequently the sutures become entirely effaced. We tire
therefore often unable to distinguish certain sclerites in one
species of insect which are distinct in another.

In such cases the effaced suture is said to be obsolete.

PARTS OF THE HEAD.

The principal portion of the chitinized parts of the head
are firmly joined together so as to constitute a box which
contains what may be called by analogy the brain of the in-
sect and certain other important organs. To this are articu-
lated a number of movable appendages. The parts of the
head may be classed, therefore, under two divisions : first,
the fixed parts, or the skull ; second, the appendages.

THE FIXED PARTS OF THE HEAD.

Compound eyes.— The most striking in appearance of
tne fixed parts of the head are the eyes. These are two large,
nearly hemispherical bodies ; one on each side, forming a
considerable portion of the latero-dorsal part of the head.

Study one of the eyes with a compound microscope, using
a low power. Note the honey-comb-like structure of the eye.
If you have difficulty in seeing this, remove a part of one eye
with fine-pointed scissors and mount it on a glass slip. Each
of the hexagonal divisions of the eye is a cornea of a distinct
eye. These large eyes are therefore compound, and each of
the small eyes of which they are composed is termed an
omniatidium (plural ommatidid)*

* Formerly the ommatidia were termed ocelli (singular ocellus] ; but later
writers use the term ocelli only to designate the simple eyes.

IO

Make a drawing showing the honey-comb-like structure of
the cornea of a compound eye.

NOTE. — The drawings illustrating this course should be made with great
care, on good paper. Outline drawings are better than those that are shaded,
as shading tends to obscure lines indicating sutures. The drawings should
be made first with a pencil, then, after they have been criticized, the lines
should be inked.

Simple eyes. — Cephalad of the dorsal half of each com-
pound eye there is a small transparent hemispherical body.
These are the simple eyes. There is a third simple eye situ-
ated in a depression near the center of the cephalic aspect of
the head. The simple eyes are termed ocelli (singular ocellus}.

Epicranium. — The larger part of the skull appears to
consist of a single sclerite which surrounds the compound
eyes, and in the locust, bears the simple eyes. This part is
termed the epicraniion. The cephalic and lateral parts of the
epicranium are separated on each side by a suture which ex-
tends ventrad from the eye. The ventral ends of these
sutures are joined by a very prominent suture which forms
the ventral boundary of the cephalic portion of the epicra-
nium.

The epicranium is a compound sclerite, and differs in its
extent in different insects.

Remove the head from the thorax and mount it on a slen-
der pin, inserting the pin in the center of the cephalic aspect
of the head. The pin will now serve as a handle.

Note the slightly elevated narrow ridge which separates
the lateral from the caudal aspect of the head. This ridge
marks the position of the suture which constitutes the caudal
border of the epicranium. Upon the dorsal aspect of the
head this suture is obsolete.

Upon each side joining the ventral end of the suture just
described and the ventral end of the one which extends ven-
trad from the compound eye is a well-marked suture, which

II

forms the ventral border of the lateral part of the epicra-
nium.

(<?.) Vertex. — The dorsal part of the epicranium is called the
vertex.

(l> ) Fro/it. — That part of the epicranium which is upon the
cephalic aspect of the head is termed t\\z front. In many in-
sects the front is a distinct sclerite.

(c.) Gena. — The lateral parts of the epicranium are known
as the gence or cheeks.

Clypeus. — Examine again the ventral border of that part
of the epicranium which is upon the cephalic aspect of the
head. Note that the prominent suture bounding this part
separates it from a very broad, but short sclerite. This is
the clypeus.

Labrum. — Articulated to the ventral border of the ciy-
peus is a broad, freely movable flap. This is the upper lip
or labrum.

Although the labrum is freely movable, it is a part of one of the segments
that enter into the make-up of the head-box, and not an appendage, like the
jaws. The true appendages of the head hold the same relation to this region
that the legs do to the- thorax.

Make a drawing of the cephalic aspect of the head ; and
name the fixed parts.

Occiput. — Examine a locust's head which has been
boiled in caustic potash, cleaned, and mounted with the
caudal aspect uppermost. In such a preparation the soft
parts have been removed, and the walls of the head bleached,
so that the sutures can be more easily traced ; a specimen
of this kind will be furnished the student.

Observe the large opening which connects the cavity of
the head with that of the thorax. The dorsal half of this
opening is bounded by the occiput. Each lateral half of the
occiput is triangular, with its outline well marked ; but on
the dorsal aspect of the head the suture between the occiput

12

and the epicranium is obsolete. Hence on this aspect there
is no indication of the line where the occiput ends and the
epicranium begins.

Postgenae. — On each side ventrad of the occiput and
caudad of the gena is a large sclerite. These form the chief
portion of the caudal aspect of the fixed parts of the head
and may be termed \\~\e postge nee.

The postgenre are separated from the epicranium by the
narrow ridge which separates the lateral from the caudal
aspect of the head ; a continuation of this ridge marks the
position of the suture which separates the occiput from the
epicranium on each side of the head.

In many insects the postgenae and the occiput are not separate. As this
is the case in the more generalized insects the occiput may be regarded as a
detached portion of the postgenas.

Tentorium. — Observe the remains of the membrane
which connected the head with the thorax. It will be seen
that the postgenae are connected by a strong part extending
from side to side, within the head. This is a part of the in-
ternal skeleton of the head or tentorium.

Make a drawing of the caudal aspect of the head, and name
the parts.

Review. — The skull of a locust consists of six sclerites ;
three of these, the occiput and the two postgence, pertain to the
caudal aspect, one, the epicranium, constitutes the greater
part of the dorsal, lateral, and cephalic aspects, and two, the
clypeus and the labnim, form the ventral portion of the cephal-
ic aspect. The epicranium consists of the vertex, \\\z front
and the genes.

Cervical sclerites. — In the membrane connecting the
prothorax with the head there is on each side a pair of scle-
rites forming a thickened line from the thorax to the head ;
these are the lateral cervical sclerites. In some insects there
are also ventral and dorsal cervical sclerites. The lateral

13

cervical sclerites are termed by some writers the jugular
sclerites.

The cervical sclerites are probably remnants of a segment the appendages
of which are modified to form the lower lip or labium.

THE MOVABLE PARTS OF THE HEAD.

Under this category are classed a pair of jointed append-
ages termed the antenna and the organs known collectively
as the mouth-parts.

Antennae. — Just cephalad of each compound eye there is
attached to the head a long, thread-like, many-jointed ap-
pendage. These are the antenna. Each antenna is situated
in a. depression which is known as the antennary fossa.

Mouth-parts.

Labrum. — Although the labrum is a part of the skull it is
commonly regarded as one of the mouth-parts.

Mandibles. — Carefully remove the labrum. By doing
this there is exposed a pair of jaws which open by a meso-
lateral motion of each jaw. These are the mandibles. Each
mandible consists of a single short and thick piece, the distal
extremity of which is notched so as to form a series of teeth.

Trochantin of the mandible. — At the base of the man-
dible, between it and the gena, there is a small sclerite ; this
is the trochantin of the mandible.

Remove the mandibles. This may be clone by separating
them with a pin and turning each one laterad until it breaks
from the head.

Maxillae. — By the removal of the mandibles there is ex-
posed a second pair of jaws which, like the mandibles, open
by a meso-lateral motion. These are the maxillce. Unlike
the mandibles the maxillae are very complicated organs. We
will return to them later.

14

Labium. — Remove the head of a locust and pin it with
the caudal aspect uppermost to a piece of cork.

Note the freely movable flap which is the caudal part of
the mouth-parts. This and the crescent-shaped piece to
which it is attached form the lower lip or labium.

The labium consists of the following parts : —

Submentitm. — The submentum is the proximal part of the
labium. It is nearly crescent-shaped, with long tapering
points, and is joined to the membrane which connects the
head with the thorax.

Mentum. — This is the central portion of the labium ; and
is the principal part of that organ. It is articulated to the
distal margin of the submentum. To the distal margin of
the mentum are joined two movable flaps ; and to each, lat-
eral margin is joined a process consisting of three segments.

Labial Palpi. — These are the three-jointed processes of
which one is joined to each lateral margin of the mentum.

Palpiger. — The labial palpi are not joined directly to the
mentum. There is on each side of the mentum a sclerite
which bears the palpus of that side and which is called the
palpiger. The suture between the palpiger of each side and
the mentum is almost obsolete. Its position is indicated by
a slight groove which causes the palpiger to appear some-
what like a segment of the palpus.

Ligula. — This is the distal portion of the labium. It con-
sists of two large movable flaps.

Hypopharynx. — If the specimen has become dry so as to
be brittle, it should be softened with a little water.

With the specimen pinned as in last section, carefully lift
the ligula so as to expose the maxillae. Note the tongue-like
organ which arises from the labium and from between the
maxillae. This is the hypopharynx.

Remove the labium and place it on a glass slip in a drop
of Canada balsam or glycerine and cover it with a cover

15

glass. Examine it with a microscope using a low power and
reflected, not transmitted, light (i.e., turn the mirror so that
the field of the microscope is dark ; and place the micro-
scope so that a strong light falls upon the specimen). Make
a drawing of the caudal aspect of the labium, and letter the
parts.

Study the distal end of the distal segment of a labial pal-
pus with a higher objective. Observe the sense papillae with
which it is furnished. Make a drawing of this part.

Parts of the maxillae. — After the removal of the labium
it is easy to distinguish the maxillae, of which there is one on
each side between the labium and the mandibles.

Remove a maxilla and mount it in Canada balsam or
glycerine, with the caudal aspect uppermost. Examine with
a microscope using a low objective, and reflected light.

Make a drawing of a maxilla, and name the parts, which
are as follows : —

Cat-do. — The cardo or hinge is the proximal part of the
maxilla. It consists of two sclerites ; the first is the larger
and is triangular in outline.

Stipes. — The stipes or footstalk is the large, quadrangular
sclerite which forms the central part of the maxilla.

Lacinia. — Articulated to the distal end of the stipes is a
large sclerite, which tapers distad, is curved, and is termi-
nated by strong teeth ; this is known as the lacinia j it is
called also the inner lobe.

Galca. — Joined to the side of the stipes near its distal end
and projecting laterad of the lacinia is a part consisting of
two segments. This is the galea. The distal segment of the
galea is large, spoon-shaped, and covers the inner lobe like a
hood ; the proximal segment is constricted in the middle so
as to resemble slightly a dumb-bell in outline. The galea is
also known as the outer lobe, upper lobe, or superior lobe.

Palpifer. — Joined to the lateral border of the stipes and

i6

between the cardoand the proximal segment of the galea is
a narrow sclerite ; this is the palpifer.

Maxillary Palpus. — Articulated to the distal end of the
palpifer is a long, slender organ consisting of five segments ;
this is the maxillary palpus,

After completing the drawing of the maxilla as a whole,
study the distal end of the distal segment of the maxillary
palpus with a higher objective, and observe the sense
papillae.

Review. — The mouth-parts consist of an upper lip, la-
bnim ; an under lip, labium ; two pairs of jaws acting later-
ally between these lips ; and a tongue-like organ, hypo-
pharynx. The cephalic pair of jaws is called the mandibles f
the caudal pair, the maxilla.

NOTE. — The natural attitude of the head of a locust is such that the la-
drum and labium appear to be fore and hind lips respectively ; and the
mandibles and maxilla, fore and hind pairs of jaws. But when the mouth
of an insect is in its more usual position, at the cephalic end of the body
axis, the labrum is an upper lip, the labium an under lip, the mandibles,
the upper jaws, and the maxillae the lower jaws.

Each maxilla consists of six parts. These are the cardo,
stipes, lacinia, palpifer, galea, and maxillary palpus.

The labium consists of the submentum, mentum, ligula, two
palpigers, and two labial palpi.

THE HEAD OF A COCKROACH.

It is desirable to supplement the study of the head of a
locust by an examination of the head of a more generalized
insect ; for this purpose a cockroach may be used. If prac-
ticable one of the larger species should be studied.

Make a drawing of the ventral aspect of the head. Owing
to the difference in attitude the ventral aspect of the head
of a cockroach corresponds to the cephalic aspect of the
head of a locust.

17

Epicranial suture. — Observe the inverted Y-shapec sut-
ure, the stem of which is on the middle line between the
compound eyes, and the arms of which extend towards the
antennae ; this is the epicranial suture.

The stem of the epicranial suture divides the vertex into
two sclerites. The arms of this suture separate the vertex
from the front, which in this case is not a part of the epi-
cranium as it is in the locust.

Antennal sclerites. — Surrounding the base of each an-
tenna there is a more or less distinct, ring-like sclerite ; this
is the antennal sclerite.

The antennal sclerites are much more distinct in the Plecoptera (stone-
flies).

Clypeo-frontal suture. — The suture separating the cly«
peus and the front is obsolete in the cockroaches. Study
this suture in the locust, and note the relation of it to the
point of articulation of the mandible with the clypeus on
each side ; and then indicate the probable position of it in
the cockroach by a faint, dotted line in your drawing.

Letter the vertex, front, clypeus, labrum, and genas.

Make a preparation showing the lateral aspect of the head
and neck, and note the following features : —

The suture separating the gena from the postgena.

The absence of a suture separating the occiput from the
postgena.

An opening into the head between the postgena and the neck
near the point of attachment of the maxilla. This is the
mouth of an invagination of the body-wall which forms a part
of the tentorium ; i.e., one of the posterior arms of the tentorium.

A narrow sclerite bounding the mouth of this invagination
on the side towards the neck ; this is one of the lateral sclerites
of the maxillary segment, the caudal one.

The maxillary segment is one of several segments that enter into the com-
position of the head, and the one of which the maxillae are the appendages.

iS

There are two sclerites on each side of the head in this segment, one on each
side of the imagination, but the cephalic one is so reduced that it can be rec-
ognized only with difficulty.

The articulation of one of the lateral cervical sclerites with
the maxillary segment.

Make a drawing of the lateral aspect of the head showing
the features mentioned above.

THE MOUTH-PARTS OF THE COCKROACH.

In the cockroach the mouth-parts are very similar to those
of the locust with an interesting and important difference in
the labium. With the named drawings of the mouth-parts of
the locust as guide, the parts of the mouth of the cockroach
can be readily determined ; the following brief notes provide
additional aid.

Labrum. — Attached to the margin of the clypeus as a
movable cuticular flap, is the subquadrangular labrum or
upper lip, serving as the dorsal or anterior covering of the
mouth. Although the position and use of the labrum makes
it one of the mouth-parts, it is morphologically different from
the other mouth-parts in not being a modified appendage.

Epipharynx. — The epipharynx of all insects is a continu-
ation or outgrowth of the upper membranous wall of the
pharynx. It is, in the cockroach, as in most insects with
biting mouth-parts, simply the ventral or internal membra-
nous wall of the labrum.

A small distal portion of the labrum of the cockroach is
rather plainly set off from the rest of the labrum by a trans-
versal suture ; it may be that this distal part is a prolonga-
tion of the epipharynx alone (a condition observable among
certain other insects). When the labrum and epipharynx are
indistinguishably fused the single organ is sometimes called
labrum-cpipharynx.

19

Mandibles. — Below the labrum-epipharynx are the strong-
ly chitinized prominent mandibles. Each mandible is a single
sclerite, toothed on its distal or biting surface.

Maxillae. — Lying next to and below the mandibles are
the maxilla:. The cardo is small and elongate, subtriangular
in shape and divided into two parts by a transverse line.
The stipes is larger, and subquadrangular. Articulating with
the stipes are the five-segmented maxillary palpus, and the
two terminal lobes, the galea and the lacinia. The galea
forms a sort of hood for the smaller triangular lacinia and is
composed of two segments. The lacinia ends in a sharp,
strong chitinous tooth. Indications, only, of the suture set-
ting off the palpiger can be discovered in the maxilla of the
cockroach.

Labium. — The labium is a single flap-like structure, which
lies below the maxilla, and forms the floor of the mouth. It
is, although an unpaired organ, really formed in all insects
by the fusion of two organs similar in character to the
maxillas. The labium is sometimes called, because of this
homology of structure, the second maxillae.

In the cockroach the proximal or articulating sclerite, the
sitbmentum, is large and shows no indication of its paired
origin. The succeeding sclerite, the mentum, is smaller and
also is without indication of an original bipartite condition.
Arising from the mentum, however, are the two four-seg-
mented labial palpi and four terminal lobes ; two of these
lobes and a palpus belong to each lateral half of the mentum
and correspond to the lacinia, galea, and palpus, respectively,
of the maxillae. The inner lobes of the labium are called
gloss a. and the outer ones, paraglossa. The glossae and para-
glossas are fused so that only their distal portions are free
and distinct. This fusion of the terminal lobes of the labium
is carried farther among most other insects. Often the
paraglossa and glossa of each side will fuse completely so

20

that there are apparently but two terminal lobes, and these
distinct only distally, or all of the terminal lobes may fuse to
form a simple flap-like sclerite, as among some of the Neu-
roptera. Because of this fusing of the bases or of all of the
terminal lobes they are often spoken of collectively as the
lignla (see p. 14. in account of external anatomy of the
locust).

Hypopharynx. — The hypopharynx is a fleshy, blunt-
pointed, tongue-like lobe, supported by a chitinized frame-
work ; this chitinous framework at the basal part of the
hypopharynx projects backwards as four slender rods, two
dorsal and two ventral, the ventral ones being curved and
shorter than the upper. This chitinous framework is called
the pharyngeal skeleton.

Make drawings of all the mouth-parts of the cockroach,
naming the sclerites.

Cervical sclerites. — Study the neck of the cockroach
and note that there are eight cervical sclerites, two dorsal,
two ventral and two on each lateral aspect.

THE PARTS OF THE THORAX.

Division into segments. — Return to the study of the
locust. The thorax consists of three segments. The cephalic
or first segment is named the prothorax ; the second or inter-
mediate, the mesothorax ; and the third or caudal, the met-
athorax.

These divisions of the thorax can be easily recognized by
the appendages they bear. To the prothorax is articulated
the first pair of legs ; to the mesothorax are joined the sec-
ond pair of legs and the first pair of wings ; and to the
metathorax, the third pair of legs and the second pair of
wings.

21

PROTHORAX.

Dorsal part (pronotum). — That which may be properly
termed the dorsal part, of the prothorax is a large sunbon-
net-shaped piece which covers the greater portion of the
sides as well as the dorsal surface of this segment. This
piece is called \ht pronotum.

It is believed that the dorsal part of each thoracic segment
consists typically of four sclerites. These are named, be-
ginning with the cephalic, prcescutum, scutum, scutellum, and
postscutellum. These sclerites may be distinguished in the
dorsal parts of the mesothorax and metathorax (inesonotum
and metanotum} of many insects; but the pronotum consists
usually of a single piece. In the insect which we are study-
ing, although the pronotum consists of a single piece, it is
crossed by three well-marked sutures, indicating the di-
vision into four sclerites, which may be named as indicated
above.

On the latero-dorsal aspect of the pronotum the suture
between the praescutum and the scutum extends cephalad
for a short distance and is then interrupted ; the lateral por-
tion of this suture is parallel with and quite near to the
cephalic margin of the pronotum. Near the center of each
lateral aspect of the pronotum there is a short oblique suture
which separates the lateral fourth of the scutellum from the
mesal part of that sclerite. None of the sutures extend to
the lateral margin of the pronotum.

Make a drawing of the lateral aspect of the pronotum.

Ventral part. — The ventral part of each thoracic seg-
ment consists typically of two sclerites, one situated in front
of the other ; the first is the sternum, the second, which has
never been named, may be termed the sternellum. The
sternellum is frequently divided longitudinally into two
parts, which may be widely separated.

22

Prosternum. — On the ventral surface of this segment
between the legs there is a sclerite which bears a large
tubercle ; this is the sternum of the prothorax or prosternum.

Prostenicllum. — The sternellum of the prothorax, or the
prosternelluni, is a narrow, transverse sclerite, which is close-
ly united to the following segment.

Lateral parts. — Owing to the great development of the
pronotum, which covers the larger portion of the sides as
well as the dorsal surface of the prothorax, the lateral parts
of this segment are rudimentary. The following named
sclerite, however, may be distinguished.

Episternuin. — Between the pronotum and the end of the
lateral prolongation of the prosternum, which extends on
each side of the segment cephalad of the leg, is a conspicu-
ous triangular sclerite ; this is the episternum.

Add the episternum to the drawing of the lateral aspect of
the pronotum.

MESOTHORAX AND METATHORAX,

Union of these segments. - -The second and third
thoracic segments are firmly joined together, forming a box
to which the two pair of wings and the second and third
pairs of legs are joined. Owing to the intimate union of
these two segments it will be easier to describe them together
than separately.

With fine pointed scissors cut away the caudal border of
the pronotum, that part which overlaps the mesonotum ; be
careful not to break the membrane connecting the protho-
rax and mesothorax.

Dorsal part (mesonotum and metanotum).- • The
dorsal part of the mesothorax is termed the mesonotum, that of
the metathorax, the metanotum. Unlike the pronotum these
parts are confined to the dorsal aspect of the body. By cut-

23

ting away the caudal part of the pronotum as indicated above
and spreading the wings laterad, these parts are exposed.
Each consists of a nearly square area. To the lateral mar-
gins of the mesonotum is articulated the first pair of wings ;
and to the lateral margins of the metanotum, the second pair
of wings.

The sutures indicating the outlines of the sclerites of
which the mesonotum and metanotum are composed, are not
well defined ; there is consequently some difficulty in deter-
mining the limits of the sclerites ; and a drawing of this part
will not be required.

In each of these segments only two of the four dorsal
sclerites are well developed ; these are the scutum and the
fcutellmn. The scutum occupies the cephalic half of the seg-
ment, the scutellum the caudal half. Thescutellum consists
of three parts : a central, shield-shaped part, which in this
species is closely united to the scutum ; and on each side a
part extending to the base of the wing. The caudal border
of the scutellum is thickened and is connected on each side
with the caudal border of the base of the wing by a cord-like
structure.

NOTE.— In those insects where the praescutum and postscutellum are well
developed, they usually extend entad and are often concealed within the
thorax. The connection of the scutellum on each side with the caudal bor-
der of the base of the wing, is an excellent guide in tracing the homology of
the parts of the mesonotum and the metanotum.

Ventral part. — On the ventral surface of the body be-
tween the legs of the second thoracic segment is a large
sclerite ; this is the sternum and the sternellum of the meso-
thorax combined. The cephalic margin of this sclerite is
nearly straight ; the caudal margin, deeply notched by a
large, nearly square incision. The part in front of this
notch is the sternum of the mesothorax or mesosterinon, the
two parts, one on each side of this notch, are the widely

24

arated halves of the sternellum of the mesothorax or meso-
sterncUum.

Caudad of the mesosternum and mesosternellum there is a
large sclerite, the mesal part of which is prolonged cephalad so
as to accurately fit the notch in the caudal border of the meso-
thorax ; this is the sternum of the metathorax or metasternum.

The two halves of the sternellum of the metathorax, or
metasternellum,wz. widely separated, each being situated near
the base of the corresponding leg.

The caudal border of the metathorax is also notched, and
the first abdominal segment is dove-tailed into it.

Cephalad of the base of each mesothoracic and meta-
thoracic leg there is a crescent-shaped sclerite ; this is the
antecoxal piece.

Make a drawing of these parts.

Lateral parts (episterna, epimera, and peritremes).
— Examine one side of the second and third thoracic seg-
ments. Note that it is chiefly composed of four large scle-
rites, which extend from the fossae of the legs dorsocephalad.
These sclerites are named as follows : —

Episternum of the mesothorax. — The first or cephalic of
these four sclerites is the episternum of the mesothorax. The
sutures between the episterna and the mesosternum are only
faintly indicated in this species.

Epimeron of the mesothorax. — This is the second of this
series of sclerites.

Episternum of the metathorax. — This is the third of this
series of sclerites ; it is the one which bears the oblique
yellow band characteristic of this species.

Epimeron of the metathorax. — This is the caudal member
of this series of sclerites.

Spiracles and peritremes. — Between the ventro-caudal angle
of the epimeron of the mesothorax and the fossa of the leg
is an organ which consists of a slit-like opening guarded by

25

two fleshy lips ; this is one of the openings of the respira-
tory system , these openings are called spiracles. When, as
in this case, a spiracle is surrounded by a circular sclerite,
such a sclerite is termed a pcritrcme.

In the membrane connecting the mesothorax with the pro-
thorax there is on each side a spiracle. This spiracle is
covered by the free margin of the pronotum. In this case
the peritreme is developed on the ventral side of the spiracle
into a prominent papilla.

Make a drawing of the lateral parts of the mesothorax and
metathorax.

Review. — The thorax consists of three segments, which
are named, beginning with the cephalic, prothorax, mesothorax,
and metathorax.

The body-wall of each of these segments is believed to
consist typically of ten sclentes. Of these,/*?*//- pertain to the
dorsal part of the segment ; tivo to each lateral part ; and two
to the ventral part.

The dorsal sclerites are named, beginning with the ceph-
alic, prcesciitum, scutum, scutellum, &\\& postscutellum.

Of the lateral sclerites, the cephalo-ventral one is the epi-
sternum, the caudo-dorsal one, the epimeron.

The ventral sclerites are known as the sternum and the
sternellitm. The sterna of the three thoracic segments are
designated as the prosternum, mesosternum, and metasternum
respectively; and the sternella as the prosternellum, mesoster-
nellum, and metasternellum.

In most insects the sternella are so reduced in size as to
be indistinguishable.

Sometimes there is also present near the base of the leg a
distinct antecoxal piece

The dorsal part of the body-wall of each segment is called
the tergum. This name is also applied to the dorsal part of
the three thoracic segments collectively.

26

The tergum of the prothorax is frequently called the pro-
notum ; the tergum of the mesothorax, the mesonotum ; and
that of the metathorax, the metanotum.

There are in this insect two pairs of thoracic spiracles.

APPENDAGES OF THE THORAX.

The appendages of the thorax are the legs and the wings ;
the number and distribution of these have already been given.

Legs. — Examine the ventral aspect of the first pair of
legs. Each leg will be found to consist of the following
named parts ;—

Coxa. — This is the proximal segment of the leg. It is sub-
globular in outline. Examine the cephalic aspect of the coxa,
and note the longitudinal suture which traverses this side of
it ; this is shown better on the mesothoracic legs.

Trochanter. — This is the second segment of the leg, and is
much smaller than the coxa. The ventral aspect of it is
much longer than the dorsal.

Femur. — This is the third and principal segment of the
leg.

Tibia. — This is the fourth segment of the leg. It nearly
equals the femur in length, but is more slender.

Tarsus. — The tarsus include-s all of that part of the leg
distad of the tibia. It consists in locusts of three segments.

The last segment of the tarsus bears a pair of claws.

On the ventral surface of the tarsus there is a series of
cushions , these are called pulvilli. The distal segment of
the tarsus bears a single pulvillus which projects between
the claws , this is often referred to in descriptive works as
the pulvillus.

NOTE. —In the membrane connecting the coxa with the thorax just ceph-
alad of the coxa, is a sclerite , this we believe to be the trockantin The
trochantin is a sclerite which is considered to be an appendage of the coxa;
and its normal position is between the coxa and the antecoxal piece

27

Make a drawing of one of the cephalic legs.

The same parts may be traced on each of the other legs.

Wings. — The wings are plate-like or membraneous ex-
pansions of the body-wall. Each wing is traversed by many
linear thickened portions ; these are termed veins or nerves.
The principal veins extend proximo-distad. These are joined
together by many smaller cross-veins. The thin parts cir-
cumscribed by the veins and cross-veins are called cells.

The two pairs of wings of a locust differ remarkably in
form and texture.

Mesothoracic wings (tegmina}. — The mesothoracic wings are
long, narrow, and of a parchment-like texture. They are
termed tegmina.

Metathoracic wings. — The metathoracic wings are much
larger and of more delicate texture than the first pair of
wings. When not in use they are folded in plaits like a fan
and concealed by the tegmina. Some writers who designate
the mesothoracic wings as tegmina or wing-covers, describe
the metathoracic wings simply as the wings.

PARTS OF THE ABDOMEN.

Number of segments — There is a difference of opinion
as to the number of segments in the body of a locust. The
difficulty arises from the complexity of the caudal end of
this region, and the fact that some authors have considered
the first abdominal sternum as a part of the metathorax.
Eight abdominal segments can be readily distinguished in
the female , and nine, in the male.* Caudad of the eighth
abdominal segment of the female and the ninth of the male

* If a sufficiently large series of specimens of the red-legged locusts be exam-
ined it will be seen that there are two kinds , one, in which the caudal part of
the body tapers to the end, and bears four, pointed find curved, horny pieces ;
and another, in which the caudal part of the body increases in size caudad
and is terminated by a single, large, hood-shaped plate. The former is the
female , the latter, the male.

28

are a number of sclerites which are considered by some
writers to be merely appendages of the abdomen ; other
writers hold that certain of these sclerites represent sterna;
and certain others, terga.

It is not within the scope of this work to enter into any
discussion of the matter. We shall describe the parts as if
there were eleven segments ; but wish the student to under-
stand that the so-called eleventh segment may be merely an
appendage of the tenth ; and that what is described here as
the ninth and tenth segments have not been considered as
such by certain very high authorities.

First abdominal segment. — The dorsal and ventral
parts of the first abdominal segment are widely separated by
the caudal part of the cavities for the insertion of the third
pair of legs.

The ventral part of this segment is dove-tailed into the
metasternum, and at first sight would be taken for a part of
the thorax.

On each side in the dorso-lateral part of this segment,
there is a large opening which is closed by a very delicate
membrane ; these are the auditory organs j the membrane is
the tympanum.

Just cephalad of each auditory organ there is a small
opening ; these are the first pair of abdominal spiracles.

Second to eighth abdominal segments.— Each of
the abdominal segments, from the second to the eighth in-
clusive, is ring-like in form, and without appendages.

In each of these segments the lateral margins of the ter-
gum join the pleura * without any suture. Near the cepha-

*The lateral part of a segment is termed the pleurum ; in the same way that
the ventral part is called the sternum ; and the dorsal part, the tcrgum. By
some writers the entire dorsal part ot an insect is called the tergum , the lateral
part, the pleurum ; and the ventral part, the sternum. These writers apply the
terms tergite, pleurite, and sternitt respectively, to the dorsal, lateral, and ster-
nal regions of each segment.

29

lo-ventral angle of each pleurutn there is a spiracle. The
sterna are well developed and are separated from the pleura
by a narrow, involuted, membraneous part.

Caudal part of abdomen of female. — The most promi-
nent portion of the caudal part of the abdomen of the
female is the ovipositor. This is an organ consisting of four,
strong, curved, and pointed pieces, which form the most
caudal part of the body. With this organ the insect makes a
hole in the ground in which she lays her eggs. This is done
by alternately bringing together and separating the two pairs
of pieces, and at the same time pushing the body into the
ground. Examine carefully these pieces, and note how well
they are adapted to this purpose.

Between the ventral pieces is the opening of the oviduct.

Ventrad of this opening and also between the ventral
pieces of the ovipositor is a pointed prolongation of the
eighth abdominal sternum ; this has been termed the egg-
guide. Dorsad of the egg-guide there is a forked organ
which also is used in placing the eggs.

The ventral pieces of the ovipositor are supported by two
pairs of sclerites ; there being a sclerite closely applied to
the ventral surface of each pair, and one to the lateral sur-
face of each.

The ninth and tenth abdominal terga are shorter than any
of the preceding abdominal terga and are joined together on
each side, the lateral parts of the suture separating them
being obsolete.

Caudad of the tenth tergum there is on the middle of the
back a shield-shaped piece ; this is believed to represent an
eleventh segment. It consists of two sclerites, as is indi-
cated by a transverse suture.

On each side, projecting from beneath the caudal border
of the tenth tergum, is a pointed appendage • these are the
cerci.

30

Each cercus partially covers a much larger, triangular
sclerite which extends from the lateral border of the tenth
tergum to the caudal apex of the eleventh tergum ; these are
the podical plates.

By lifting the free end of the eleventh segment, the cau-
dal opening of the alimentary canal, the anus, is exposed ; it
is situated between the podical plates.

Caudad of the podical plates is the dorsal pair of pieces of
the ovipositor.

Make drawings of the dorsal and the lateral aspects of this
part of the body ; in the drawing of the lateral aspect repre-
sent the entire abdomen.

Caudal part of the abdomen of the male.— In the
male ten abdominal sterna are present ; the tenth is a hood-
shaped sclerite on the caudal aspect of the body.

As in the female, tho ninth and tenth abdominal terga are
united on their lateral margins.

Projecting from the caudal margin of the tenth tergum
there is on the middle of the back a forked appendage, the
furcula.

The eleventh tergum is furrowed by three deep longitu-
dinal grooves.

The cerci are situated as in the female, but are longer.

The podical plates are nearly as in the female.

Make drawings of the dorsal and the lateral aspects of
this part of the body.

CHAPTER III.

THE INTERNAL ANATOMY OF AN INSECT.
Corydalis cormita.

The larva of Corydalis cornuta lives under stones in the bed
of swiftly flowing streams ; it is well known to sportsmen
under the name of " dobson," and is used extensively as bait
for black bass.

As the larval state of Corydalis lasts nearly three years,
larvae which are at least two years old may be found at any
time. They are most abundant where the water flows swift-
est. A good way to obtain them is to hold a dip-net or a
wire screen in the stream below some stones, and, lifting the
stones with a hoe or garden rake, cause the current to sweep
into the net the insects which were under the stones.

This larva is probably as desirable a subject for an ele-
mentary study of the internal anatomy of insects as can be
found in this country. The species is a large one, being one
of our largest insects ; there is a coarseness in its structure,
which enables one to study the different viscera with com-
parative ease ; it is furnished with well-developed organs for
aquatic respiration, and at the same time with equally well-
developed organs for aerial respiration ; and, as already
stated, fresh specimens can be easily obtained at any season,
even in mid-winter.

Unfortunately, however, the appearance of the insect is
very disagreeable to most people. But after a specimen has
been opened and pinned upon cork, as is necessary in the
study of the viscera, the disagreeable features are not visible ;

31

32

and the ease with which the internal organs can be examined
more than counterbalances the unpleasant part of the prepara-
tion of specimens.

PRESERVATION OF SPECIMENS.

Specimens that are to be used for the study of internal
anatomy should be preserved in an aqueous solution of chlo-
ral hydrate ; this is made by dissolving one part by weight of
chloral hydrate in twenty parts of water. This liquid pre-
serves the organs and at the same time leaves them flexible.
After the specimens have been in the solution for one day, a
short, longitudinal slit must be made through the wall of the
abdomen, so as to allow the solution to enter the perivisceral
cavity ; otherwise the viscera will decay. The delay of one
day before making the slit in the body is important ; if the
slit is made too soon, the muscles will contract in such a way
as to distort the specimen and render it worthless. One-half
of the specimens should be slit on the back, the others, on
the ventral side ; for if the specimens are all cut in the same
manner, it will be impracticable to study certain organs.

If a very careful study is to be made of the external anat-
omy of this larva, one or more specimens should be left for
several days in a warm place, in the chloral hydrate solution,
without being cut. The parts bathed by the solution will be
well-preserved ; the viscera will decay ; and the gases of de-
composition will so distend the body that the different scle-
rites will be spread apart.

EXTERNAL CHARACTERISTICS.

In order to understand the internal anatomy of this insect
it is necessary to know the more general features of its ex-
ternal anatomy. We will not stop to trace out the homol-
ogies of the different sclerites which enter into the compo-

33

sition of the body-wall, but will merely examine the more
important external structures.

Pin a larva to the cork or beeswax lining of a dissecting
dish, with its ventral aspect uppermost, and cover it with
water. Make a drawing of the ventral surface. Name the
regions and the appendages of the body shown in this view.
The long, tapering appendages on the margins of the abdo-
men may be termed the lateral filaments ; the tufts of hair —
like appendages near the bases of the lateral filaments are
tracheal gills ; and caudad of the ninth abdominal segment
is a pair of prolegs. These may be termed the anal pro-
legs*

Make a drawing of each of the following parts : —

1. The dorsal aspect of the head, showing the mandibles,
the antennae, and the labrum.

2. One of the tracheal gills. Cut off several of the hair-
like branches and mount them in glycerine, using a thin
cover-glass. Examine them with a compound microscope,
using a high power. The surface of each hair is marked
with numerous ridges, which resemble in appearance the fine
ridges on the skin of the palm of the human hand. In the
center of each hair, and extending nearly its entire length, is
a large tube. This is a trachea or air vessel. Tracheae can
be distinguished from other vessels by being marked with
transverse lines, which occur at regular and very short inter-
vals. The intimate structure of the trachea; will be studied
later ; but at this point the student should become familiar
with the appearance of tracheae, so that when he dissects the
insect he can readily distinguish them from other vessels.
Branching from this large central trachea are numerous very

*Many larvag bear upon the abdomen locomotive appendages, which resem-
ble legs, and are termed prolegs. This is especially true of caterpillars, which
bear from one to five pairs of these appendages. The prolegs are temporary
organs, being shed with the skin when the larva transforms to a pupa.

34

small tracheae. Carefully trace out the courses of the small
tracheae and represent them in your drawing.
3. A spiracle.

INTERNAL ANATOMY.

Preliminary work. — Take from the chloral hydrate
solution a specimen which was slit on the ventral surface.
Immerse the insect in water, with its dorsal surface down-
wards. With fine scissors extend the slit the whole length
of the thorax and abdomen ; in making this slit cut through
the wall of the body into the perivisceral cavity ; the body-
wall consists of two parts, the external crust of the insect,
and, entad of this a wall of muscles; it requires consider-
able care to cut into the perivisceral cavity and not injure
the viscera. Make, on each side, in that part of the body-
wall connecting the prothorax with the head, an incision
extending from the longitudinal incision to the side of the
body.

On the meson just entad of the ventral wall of the body,
there are two white cords, extending nearly the whole
length of the- body. At intervals, which approximate the
segments in length, these cords are united ; at the points of
union they are greatly enlarged ; from these enlargements
there arise numerous, small, white cords, which extend in
various directions. The two longitudinal cords, the en-
largements upon them, and the numerous cords branching
from these enlargements constitute the nervous system ; the
cords are nerves and the enlargements are ganglia. The
nervous system will be studied later in a specimen which
has been opened on the dorsal side.

Cut away from the ganglia the nerves that extend to one
side ; do this with the scissors, first placing one blade under
the nerves and lifting them away from the other viscera.

Take a strip of sheet-cork a little longer than the insect

35

and twice as wide, and pin it to the beeswax lining of the
dissecting dish, and cover it deeply with water. Place the
specimen on the cork and fasten with a pin at each end.
Turn laterad each half of the ventral wall and pin it down to
the cork, using ribbon-pins.

NOTE. — At the close of the day's work on this subject the student should
remove the strip of cork from the dissecting dish and place it with the speci-
men still spread out upon it in a wide-mouthed bottle of chloral hydrate
solution. By doing this the work can be resumed without the necessity of
making a new dissection.

Ramifying through all parts of the body are numerous
trachea ; the larger trachea? are of a dusky color ; but many
of the smaller ones contain air, which renders them silvery
white. On each side of the body, extending the entire
length of the thorax, are two very large trachea? ; from each
side of each abdominal segment except the last there arises
a large trachea, which divides and subdivides into numerous
branches. Cut a short piece from one of the large abdom-
inal trachea?, examine it with a compound microscope, and
note its characteristic appearance, so as to be able to distin-
guish trachea?.

In the dissection of this specimen, the student may cut
trachea? and nerves freely ; but great care should be used
not to cut other vessels unless specially directed to do so.

In the center of the perivisceral cavity and extending the
whole length of the body, there is a large tube ; this is the
alimentary canal.

Adipose tissue. — Surrounding the caudal half of the
alimentary canal and attached to the lateral and dorsal walls
of the abdomen and thorax, there are large, flocculent
masses of a white substance ; this is the adipose tissue or fat.

Examine a preparation of adipose tissue, with a compound
microscope, using a high power, and make a drawing sho\v>
ing the rmnute structure of the tissue.

36

In the farther dissection of this specimen the adipose
tissue may be cut away when necessary to see the parts
studied.

Form of the alimentary canal. — Remove the ventral
wall of the head so as to expose the alimentary canal
throughout its entire length.

Make a drawing of the alimentary canal and label the fol-
lowing parts : —

Pharynx. — The somewhat trumpet-shaped part of the
alimentary canal immediately caudad of the mouth is the
pharynx.

(Esophagus. — That part of the alimentary canal which is
immediately caudad of the pharynx and which traverses the
caudal part of the head and the cephalic part of the thorax
is the (Esophagus. It is a straight tube of nearly uniform
diameter except when some portion of it is distended by
food.

Proventriculus, — In the caudal part of the thorax the
alimentary canal begins to enlarge. This enlargement in-
creases gradually caudad until, in the first or second abdom-
inal segment, its diameter is twice that of the oesophagus ;
then it contracts quite suddenly until its diameter is less
than that of the oesophagus ; this enlarged portion is the
proventriculus. It corresponds in function with the gizzard
of birds and is very complicated in structure internally.

Ventriciilus. — Caudad of the constriction following the pro-
ventriculus, there is a slightly enlarged portion, from the
cephalic end of which there project cephalad, four large
pouches; this enlargement is the ventriailus or sto macJi and
the pouches are the gastric cceca. The two caeca of each
side are quite closely united.

Malpighian vessels. — Emptying into the caudal end of the
ventriculus are several, small, very long, and much convo-
luted tubes ; these are the Malpighian vessels ; they were

37

named in honor of Malpighi, one of the early anatomists.
As uric acid is found in the Malpighian vessels, they are
supposed to correspond to the kidneys in function.

Determine the number of Malpighian vessels.

Intestine. — The part of the alimentary canal extending from
the ventriculus to the caudal end of the body is the intes-
tine ; the part immediately caudad of the ventriculus is the
small intestine ; following the small intestine is the large
intestine ; there are two bends in the cephalic part of the
large intestine ; the first extends dorsad and cephalad ; the
second, dorsad and caudad ; the rectum is not a well-defined
part of the intestine in this insect.

Attachments of the alimentary canal. — The alimentary canal is
attached to the body-wall and thus held in place in various ways. The
most obvious attachments are those of the ends of this organ. In addition
to these direct connections, the alimentary canal is indirectly connected to
the body-wall as follows: —

By trachecE. — From the lateral wall of each abdominal segment, large
tracheae arise ; many of the minute branches of some of these extend to the
walls of the alimentary canal and thus tend to hold it in place.

In connection with the tracheae, the action of the masses of adipose tissue
should be observed. These large masses, which to a great extent are held
in place by the tracheae that extend to the alimentary canal, serve as cushions
which tend to keep the organ in place.

By muscles. — A large number of very delicate muscles extend from the
ventral wall of the head to the oesophagus. In the specimen which the stu-
dent is now studying, only the ends of these muscles which are attached to
the oesophagus can be observed, as the attachments of these muscles to the
wall of the head were cut away in the preparation of the specimen. Large
muscles extend caudo-ventrad to the intestine from the line on the dorsal wall
of the body between the eighth and ninth abdominal segments. From
within the anal prolegs, muscles extend cephalad into the ninth abdominal
segment and are attached to the intestine. Other muscles are described in
the next section.

By the suspensoria of the viscera. — There are several, long, fine threads
that are so attached as to tend to hold the alimentary canal and other viscera
in place. These may be termed collectively the suspensoria of the viscera.

38

In Corydalis four pairs of suspensoria can be distinguished. There are two
pairs of suspensory muscles, a pair of ligaments, and a pair of suspensory
nerves.

The suspensory muscles arise from the body-wall in the thorax, and ex-
tend caudad into the abdomen, where both pairs are attached to the aliment-
ary canal, and one pair to other viscera also. It is rather difficult to trace
out the origins of these threads upon the body-wall ; but the threads can be
easily seen extending parallel with the oesophagus and proventriculus, after
they emerge from the layer of muscles and fat. They can be rendered more
easily seen by staining the specimen with haematoxylin. Empty the water
from the dish containing the specimen, and place a few drops of hasmatoxy-
lin on it ; after one or two minutes wash off the stain, and cover the speci-
men with clean water.

Study first the suspensoria on one side of the specimen, leaving those of
the other side for study when the final drawing is made. In the following
notes a single member of each pair of suspensoria is described.

The two suspensory muscles may be designated as the simple suspensory
muscle and the branched suspensory muscle, respectively.

The simple suspensory muscle arises from near the middle of the ental
surface of the pronotum, and extends caudad to the gastric caeca, where the
fibers of which it is composed spread apart, some going to one caecum and
some to the other.

Make a provisional sketch of this.

With fine-pointed scissors, cut off the tips of the two gastric caeca of this
side, and remove them with as long a piece of the suspensory muscle as is
practicable, and mount them in glycerine for study with a high power of the
microscope. Note the transversely striated appearance of the fibers of this
suspensorium. This indicates that it is composed of striated muscular tissue.
Make a careful drawing showing the minute structure of this suspen-
sorium.

The branched suspensory muscle arises from the ental surface of the body-
wall, on the dorsal side, between the mesothoracic and metathoracic shields,
near the lateral margin of the body and extends caudad into the cavity of
the abdomen ; here it divides into several branches. One branch extends
to the ventriculus ; one or more to the masses of fat and to the Malpighian
vessels ; and one joins a suspensorium which extends from a large trachea
hi the third abdominal segment to the intestine.

Trace out the course of the branches of the branched suspensory muscle,
and make a provisional sketch showing their connections.

39

The ligament of the viscera is not attached to the body-wall, but is sup-
ported by a large trachea in the third abdominal segment, about which it-
forms a collar. This suspensorium has three branches ; one of these ex-
tends caudad to the testis or ovary ; one, cephalad, to the heart ; and the
third, to the intestine. This last branch receives the tendon of one of the
branches of the branched suspensory muscle.

Make a drawing representing the alimentary canal in the center, a testis or
ovary on each side (these are described in the next section), and the three
pairs of suspensoria. While doing this the provisional sketches already
made can be utilized, but the observations should be confirmed by a sfudy
of the suspensoria of the other side of the specimen.

Cut the trachea supporting the ligament of the viscera, and slip the liga-
ment off from it ; cut the ligament extending to the heart as near to the
heart as practicable ; cut the ligament extending to the intestines between
the intestine and the tendon of the branched suspensory muscle ; cut the
branched suspensory muscle as far cephalad as practicable ; cut off the tip
of the testis or ovary, leaving it attached to the ligament ; mount the prepa-
ration thus made in glycerine for study with the microscope, carefully spread-
ing apart the branches of the ligament and the end of the suspensory muscle
with a needle before putting on the cover-glass. Study this preparation
with a high power of the microscope and note the difference in structure
between the suspensory muscle and the ligament of the viscera. Make a
drawing showing this.

The suspensory nen<es of the alimentary canal extend from the small in-
testine to the last abdominal ganglion. They can be best seen in a speci-
men opened on the back and will be described later.

The masticatory organs of the proventriculus.-

Remove the alimentary canal, and carefully open the proven-
triculus by a longitudinal slit. Cover a piece of cork with
white paper, spread out the opened proventriculus upon the
paper, ental side uppermost, and fasten it in place with rib-
bon-pins. Fasten the cork bearing the preparation to the
beeswax in a dissecting dish, and cover the preparation
with water. Study it with a lens and with a compound
microscope, using a low power. Write a description of
the masticatory organs, and make a drawing illustrating
them.

40

The reproductive organs. — Although there appears to
be no external characteristic by which the sexes of the larva
of Corydalis can be distinguished, the internal reproductive
organs differ greatly in appearance ; the testes in this species
are long and narrow, while the ovaries are short and broad.
These organs are situated one on each side, between the
layer of adipose tissue which surrounds the alimentary canal
and the layer of the same tissue which is attached to the
sides of the wall of the abdomen. The testes extend from
near the middle of the third abdominal segment to near the
posterior border of the sixth abdominal segment. The ova-
ries extend from near the middle of the fourth abdominal
segment to near the middle of the fifth abdominal segment.

Determine the sex of the specimen that you are studying.

Reproductive Organs of the Male. — Note the shape of a testis, the con-
nection of it with the respiratory system, the groove in the middle of its
mesal aspect, and the vessel in the bottom of this groove. This vessel is the
seminal duct or vas deferans (plural, rasa deferentia) and is the outlet of
the testis ; it extends caudad to near the caudal end of the body. The
cephalic end of the testis is supported by the ligament of the viscera already
described.

Make drawings showing the external form of a testis.

Trace out the course of the vas deferens. This will require very careful
dissection, especially in the ninth abdominal segment, where the vas defer-
ens passes under a muscle.

The triangular organ into which the two vasa deferentia empty is the
seminal vesicle. If the specimen has been opened on the ventral side, the
seminal vesicle will lie on the alimentary canal, but if it has been opened on
the dorsal side it will be necessary to cut the intestine and turn back the
caudal part of it in order to see the seminal vesicle.

The tube extending from the seminal vesicle to the external opening of
the reproductive organs is the ejaculatory duct.

Make a drawing showing the relations of the testes, vasa deferentia, semi-
nal vesicle, and ejaculatory duct.

Each testis is composed of many, short, pear-shaped tubes, the testicular
follicles, in which the spermatozoa are developed. These tubes open into

the vas deferens, which, as already described, extends along the groove in
the testis. The testicular follicles, however, are enclosed in a thick coat of
connective tissue which conceals them.

Reproductive Organs of the Female. — Note the shape of an ovary, the
connection of it with the respiratory system, the position of the oriduct
(which is the vessel extending caudad from the ovary), and the attachment
of the ligament of the viscera.

Make a drawing showing these things.

Each oviduct extends caudad from the caudal end of the ovary through
masses of fat to the seventh abdominal segment, where, at a point opposite
the last ganglion of the nervous system, it passes under the ventral muscles,
and terminates in a disc-like enlargement, on the body-wall.

Make a dissection showing this.

NOTE. — In the adult the two oviducts extend caudad to near the caudal
end of the body where they empty into a short vagina.

Each ovary is composed of many parallel tubes, the egg-lubes, in which
the eggs are developed, and which open into the oviduct. But as the
egg-tubes are enclosed in a thick coat of connective tissue, which en-
velopes the entire ovary, it is necessary to break this coat in order to see
them.

Remove an ovary, place it on a glass slip, tease it apart with needles, and
examine it with a microscope.

Make a drawing of an egg-tube.

The reproductive organs of a locust. — As the repro-
ductive organs of the larva of Corydalis are in an immature
condition, it will be well for the student to study, at this
point in his work, the reproductive organs of an adult insect.
For this purpose the red-legged locust may be used. If pos-
sible use fresh specimens.

The reproductive organs of the male. — Remove the wings
and legs from an adult male locust, make a slit in the dorsal
wall of the body, extending the whole length of the thorax
and abdomen, spread open the specimen, pin it to a piece of
cork, and place it under water for dissection.

The testes lie upon the stomach, and are enclosed in a com-
mon sack-like envelope. This is exceptional ; in most in-

42

sects the two testes are separate, each lying in one side of
the body-cavity.

The cephalic end of the united testes is supported by the
ligament of the viscera, which is a very slender cord, extend-
ing to the dorsal wall of the body.

Break the envelope enclosing the testes and note that they
are composed of many, long, slender tubes ; these are the
testicular follicles.

Separate the two sets of follicles and observe that those of
each side empty into a slender duct ; this is the vas deferens.
The two vasa deferentia pass caudo-ventrad, one on each
side of the alimentary canal.

Cut in two the alimentary canal between the testes and
remove the caudal portion of it.

Observe the two bundles of tubes which occupy a consid-
erable part of the cavity of the abdomen ; these are the semi-
nal vesicles and the accessory glands. There is on each side a
single, long, much convoluted, accessory gland, and a bundle
of shorter, tubular seminal vesicles. The seminal vesicles are
reservoirs for the products of the reproductive organs ; the
function of the accessory glands has not been determined,
they may secrete the more fluid part of the semen.

Trace out the course of the vasa deferentia, and note that
each is joined by the seminal vesicles, and the accessory
gland of the same side, and that almost immediately the tubes
of the two sides unite, forming a single tube ; this is the
ejaculatory duct.

The ejaculatory duct leads to the penis ; owing to the
muscles surrounding this organ the determination of its form
is quite difficult, and will be omitted in this elementary course.
If fresh specimens are available, kill one in a cyanide bot-
tle, and by pressure of the abdomen force out the caudal end
of this organ, and observe the chitinous hooks with which it
is armed.

43

Dissect another specimen, opening it on the ventral side.

Make a diagram representing the relations of the various
parts of the reproductive organs of the male locust.

If fresh specimens can be obtained, kill one, remove a
seminal vesicle from it, tease apart the vesicle on a glass
slip, mount it in glycerine, examine it with a high objective,
and observe the bundles of spermatozoa. Each bundle con-
sists of a great number of hair-like spermatozoa.

The reproductive organs of the female. — Take an adult
female locust, remove the wings and hind legs, and make a
slit in the dorsal wall of the body extending the whole length
of the thorax and abdomen. Spread open the specimen, pin
it to a piece of cork, and place it under water for dissection.

The ovaries lie above and on each side of the stomach :
the cephalic end of them is supported by the ligament of the
viscera. The egg-tubes of which the ovaries are composed
occupy the same relative position as the testicular follicles of
the male, but fill a larger proportion of the body-cavity.

Push laterad the egg-tubes of each side so as to expose
the alimentary canal ; cut in two the alimentary canal in the
thorax, and remove the caudal portion of it ; this will expose
two large bundles of muscles connected with the dorsal pair
of valves of the ovipositor. Carefully split these apart and
fasten them aside with pins. When this is done, the last
ganglion of the nervous system will be exposed. Carefully
remove this ganglion, cutting such nerves and tracheae as
may be necessary.

Each ovary consists of many egg-tubes which are arranged
in two rows, and open into an oviduct ; the two oviducts unite
near the caudal end of the body and form the common ovi-
duct or vagina.

That portion of each oviduct into which the egg-tubes
empty is greatly enlarged ; this is termed the egg-calyx, and
serves as a receptacle for the ripe eggs.

44

There is a prolongation of each oviduct which extends
cephalad of the ovary ; this, we infer is a colletcrial gland.
The colleterial glands are organs which secrete the cement
for gluing together the eggs ; the more usual form of them
is that of separate glands, like the accessory glands of the
male, which open into the vagina, as the accessory glands
open into the ejaculatory duct.

Lying dorsad of the vagina, there is a small elongate body,
from which there extends a much convoluted tube ; these
are the spermathcca and its duct.

On each side of the vagina, near the caudal end of the
body there is a rounded pouch, which in fresh specimens is
of a reddish color. From the cephalic end of each pouch a
muscle passes cephalad along the dorsal wall of the vagina,
and between the two oviducts, and is attached to the ventral
wall of the body. These pouches open below the ventral
valves of the ovipositor, one on each side of the opening of
the vagina, but a little farther dorsad than that opening.
The function of these organs has not been determined ;
they are described here on account of their intimate rela-
tions with the reproductive organs. They are doubtless
eversible glands, as in fresh specimens they can be everted
by pressure ; and the muscles are doubtless for withdrawing
them after eversion.

If living specimens are available, kill a female, by putting
it in a cyanide bottle, and then by pressure of the abdomen
evert these glands. Note that they open separately between
the last sternum of the abdomen and the ventral valves of
the ovipositor.

Take a fresh specimen, or a preserved one, if fresh speci-
mens are not to be had, and spread apart the last sternum
of the abdomen and the ovipositor, and observe the elliptical
opening between the ventral valves of the ovipositor. This
opening is surrounded by narrow bands of chitin, and is

45

the opening of the bursa copulatrix. It is through this opening
that the seminal fluid is received.

The opening of the vagina is distinct from that of the bursa
copulatrix, and ventrad of it. It is on the dorsal aspect
of the lobe of the body supported by the last abdominal
sternum.

Return now to the study of your dissection.

Trace out the course of the duct leading from the sperma-
theca and observe that it empties into a pouch ; this is the
bursa copulatrix, the external opening of which has been ex-
amined already.

Trace out the course of the vagina and observe that its
opening is distinct from that of the bursa copulatrix, as has
been pointed out.

When the eggs are laid they are pushed dorsad past the
opening of the bursa copulatrix, in this way spermatozoa
coming from the spermatheca can reach them. The egg-
shell of insects is perforated at one end by one or more
openings, the micropyle through which a spermatozoon passes
to fertilize the egg.

Dissect another specimen, opening it on the ventral side.

Make a diagram representing the relations of the parts of
the reproductive organs of a female locust.

Review.— The following tabular statement will aid the
student in making a review of his work on the reproductive
organs of a locust, and will serve to indicate the correspond-
ence of the parts in the two sexes. He should bear in mind,
however, that the reproductive organs of different insects
vary greatly in structure. In most insects each testis or
ovary consists of many parallel tubes, as in the locust ; but
the structure and position of the reservoirs of the products
of these organs and the structure of the accessory glands
differ greatly in different insects.

REPRODUCTIVE ORGANS OF A LOCUST.

I. MALE.

1. Two testes, each testis consisting

of many testicular follicles.

2. Two vasa defercntia.

3. Several seminal vesicles, each

an appendage of a vas def-
erens.

4. Two accessory glands, each an

appendage of a vas def-
erens.

5. An ejaculatory duct, the united

vasa deferentia.

6. A penis.

II. FEMALE.

1. Two ovaries, each ovary consist

ing of many egg-tubes.

2. Two oviducts.

3. Two egg-calyces, each calyx an

enlarged portion of an ovi-
duct.

4. Two colleterial glands, each a

cephalic prolongation of an
oviduct.

5. A vagina, the united oviducts.

6. An ovipositor.

7. A bursa copulatrix and a sper-

matheca with a duct connect-
ing them.

The respiratory system. --Return to the study of
Corydalis. Make a diagram showing the arrangement of
the larger tracheae.

The walls of the tracheae are
composed of three layers, which
correspond to the layers of the
body-wall ; in fact the tracheae
are invaginations of the body-
wall. The continuity of the
membranes of the tracheae and
body-wall is shown diagrammat-
ically in Figure i. It should
be observed that it is the inner
layer of the wall of the tracheae
that corresponds with the outer
layer of the wall of the body.

This inner layer of the wall of
the trachea, the intima, like the
cuticle, is chitinous, and is shed
from the tracheae with the cuticle when the insect molts.
This layer of the trachea is furnished with thickenings, which

FIG. i. — Section of trachea and
body-wall, c, cuticle ; hy^ hypo-
dermis ; sp, spiral thickening of
the intima. The third layer is
a delicate membrane bounding
the ental ends of the hypoder-
mal cells ; this is the basement
membrane.

47

extend spirally and give to tracheae their characteristic,
transversely striated appearance. If a piece of one of the
larger tracheae be pulled apart the intima will tear between
the folds of the spiral thickening, and the latter will uncoil
from within the trachea like a thread. These spiral thicken-
ings are termed tanidia (Greek, little bands). In some insects
there are several, parallel thickenings of the intima, so that,
when an attempt is made to uncoil the toanidia, a ribbon-like
band is produced, which is composed of several parallel taenidia.

Make a preparation and a drawing illustrating the appear-
ance of a trachea of Corydalis, with the taenidia partially
uncoiled.

The heart and the aorta. — Read the account of the
blood-vessels in CbmstocKs Manual for the Study of Insects,

PP- 7i, 72.

In Corydalis the dorsal blood-vessel extends from the
eighth abdominal segment to the brain. It is a slender tube,
widest in the region of the fourth and fifth abdominal seg-
ments. That part of it which lies in the abdomen is the
heart ; the more slender portion which traverses the thorax
and extends into the head is the aorta.

The cephalic end of the aorta is attached to the brain, and
is trumpet-shaped except that the ventral wall of it is split.
In this way a V-shaped opening is formed, through which
the blood flows out, into the cavity of the head.

Make a drawing representing the outline of the heart and
the aorta.

The valves of the heart and of the aorta. — Usually it is very diffi-
cult to determine the position and form of the valves in the dorsal blood-
vessel in specimens preserved in chloral hydrate solution ; for a study of
these valves specimens which have been prepared especially for this pur-
pose are necessary. On this account this part of the subject may be omit-
ted by students taking a brief course in entomology. For the sake of
others the following method of study is indicated :

48

With a hypodermic syringe inject into the body-cavity of a living larva a
solution of lampblack or of carmine.* After about an hour, drop the larva
into boiling water and leave it there till killed, which will require from ten
to twenty seconds ; then transfer it to cold water. In specimens prepared
in this way the heart will be found n-lled with coagulated blood, which is
rendered more easily seen by the presence in it of the lampblack or carmine.
The relation of the valves to the segments of the body can be best deter-
mined in specimens from which the dorsal body-wall has been removed
from over the heart, the specimens being studied from the dorsal aspect.

In Corydalis the heart contains eight sets of valves, and the aorta two.

Make figures showing the position and form of the valves of the heart
and of the aorta.

The pericardial diaphragm or the "wings of the
heart." — Take the specimen which was prepared so as to
show the heart and the aorta. Empty the water from the
dish containing the specimen, and place a few drops of
haematoxylin on it ; after one or two minutes wash off the
stain, and cover the specimen with clear water. Careful
examination will now reveal the dorsal diaphragm, which is
so delicate that it is seen with difficulty unless stained.

This diaphragm is attached along its middle line to the
ventral surface of the heart. Each lateral edge of the
diaphragm is attached to the body-wall in sixteen places,
along two lines.

Represent the pericardial diaphragm upon the drawing of
the heart and aorta already prepared.

There are differences of opinion as to the function of the
pericardial diaphragm. f It seems to us that an important
function, if not its chief function, is to protect the heart
from the peristaltic movements of the alimentary canal. It
also supports the heart ; and may play a part in its expan-
sion.

•
*.2 g. lampblack, .2 g. gum arabic, 15 c. c. water; or .4 g. carmine, .2 g.

gum arabic, 15 c. c. water.

t See Packard. Text Book of Entomology, pp. 401, 402.

49

Review. — Take a specimen that has been slit on the
dorsal surface and make a preparation similar to the one just
studied except that it is opened on the back. Review the
work on internal anatomy indicated above excepting those
parts referring to the nervous system, which will be con-
cealed by the alimentary canal in this specimen, and to the
circulatory system, which will be destroyed in the prepara-
tion of the specimen.

Note especially the form of the reproductive organs and
determine if the specimen is of the same sex as the one pre-
viously studied. If it is not, complete the work on the re-
productive organs indicated above ; if it is of the same sex,
other specimens should be examined after the work on this
one is completed.

The suspensory nerves of the alimentary canal. — Gently push
the intestine to one side and note the two fine threads extending caudad
from the small intestine. Trace out the connection of these threads or
nerves with the nervous system. Note the fine branches of these nerves
that extend to the caudal part of the intestine.

Make a diagram representing a side view of that part of the alimentary
canal caudad of the proventriculus, the last three ganglia of the nervous
system, and the nerves just described.

The ventral diaphragm. — Cut the alimentary canal in
two between the ventriculus and the first bend in the intes-
tine. Remove that part of the alimentary canal caudad of
this point. Cut the tracheae of one side extending to the
remaining part of the alimentary canal, so that it can be
pushed away to the other side. Be careful not to injure this
part of the alimentary canal till after the vagus nerve has
been studied, as indicated in a later paragraph. Empty the
water from the dish containing the specimen and put a few
drops of hasmatoxylin solution on the muscles and nerves in
the abdomen ; after one or two minutes, wash off the stain,
and cover the specimen with clear water ; observe the ven-

50

tral diaphragm. This is a transparent, apparently structure-
less membrane, stretched over the floor of the abdominal
cavity in such a way as to protect the central part of the
nervous system. Owing to the transparency of this mem-
brane, it is very difficult to see it unless it is stained. The
ventral diaphragm is attached along each side of the body
just laterad of the great ventral muscles ; the points of at-
tachment are on the lines separating the segments of the
body. Between the points of attachment, the margins of
the membrane curve mesacl, giving it the appearance of be-
ing strongly stretched at the points of attachment.

This diaphragm has been described as a ventral heart.
See Packard, Text Book of Entomology, p. 403. We believe its
function is to protect the central nervous system from the
peristaltic movements of the alimentary canal.

The nervous system. — After removing the alimentary
canal from the specimen opened along the back, the central
nervous system will be exposed.

Make a diagram showing the disposition of the ganglia
and of the principal nerves of the thorax and abdomen.
These can be seen better in a specimen which has been
opened along the venter. Take for this purpose either a
fresh specimen or one that has been slit on the dorsal side,
and open it carefully on the ventral side so as to cut through
only the body-wall, leaving the nervous system in place.

Make careful dissections of the ganglia and nerves found
in the head, and make a diagram showing their arrangement.

The following parts should be observed and figured : —

The siipracesophageal ganglia. — These are two, large, ovoid
ganglia, lying above the oesophagus, and connected by a
short, thick commissure. They are sometimes termed the
brain.

The antennal nerves. — These arise from the latero-cephalic
angles of the supracesophageal ganglia.

The optic nerves. — These arise caudad of the origins of
the antennal nerves. Determine the number of divisions of
each optic nerve.

The crura cerebri. — These are the two, large cords, one on
each side, connecting the supracesophageal ganglia with the
subcesophageal ganglion, and forming with these ganglia the
nervous collar of the oesophagus. (The singular form of
crura is cms.)

The vagus nerve. — Just cephalad of the supracesophageal
ganglia there is a minute ganglion, the frontal ganglion;
this is connected by an arching nerve on each side with the
crura cerebri ; from the frontal ganglion there extends ceph-
alad a small, branching nerve ; from the frontal ganglion
there also extend two nerves which pass caudad ; one of
these extends to the commissure connecting the supra-
cesophageal ganglia ; the other passes between the supra-
cesophageal ganglia and the oesophagus, and ventrad of the
aorta (which is usually turned to one side in opening the
specimen as this one is opened), to a minute ganglion on the
middle line of the oesophagus, caudad of the supracesopha-
geal ganglia. From this minute ganglion two nerves extend,
one on each side, to the sides of the alimentary canal, which
they follow to the proventriculus, where they divide into
many branches. This system of nerves and ganglia is
termed the vagus nerve.

The subcesophageal ganglion. — This is the large ganglion on
the meson, ventrad of the oesophagus. From it two large
cords pass caudad to the first thoracic ganglia.

From the subcesophageal ganglia nerves extend to the labi-
um, the maxillae, the mandibles, and to other parts of the head.
The beginning students who are taking a short course in ento-
mology need not trace out these nerves. Other students may
use as a work of reference a paper on this subject by Dr.
William C. Krauss, published in "Psyche" vol. IV., pp. 179-184.

52

The muscular system. — In a fresh specimen the mus-
cles appear soft and translucent ; but in specimens that have
been kept for a considerable time in a preservative fluid,
they are firm and opaque. The greater number of the mus-
cles are attached to the ental surface of the body-wall where
they form several layers. This is well shown in the abdo-
men, where most of the muscles are for moving the seg-
ments of the body. In the head and thorax, there are
numerous muscles for moving the appendages of the body,
and their arrangement is much more complicated.

To attempt to make a detailed study of the muscular sys-
tem would require much more time than can be devoted to
this system in this elementary course. Only the more gen-
eral features of the structure of the muscles and of their
arrangement will be noticed.

Note that the muscular system is composed of an im-
mense number of distinct, isolated, straight fibers, which are
not enclosed in tendinous sheaths as they are with verte-
brates.

Mount a few of these fibers in glycerine, and study them
with a high power of the microscope. Note that the fibers
present numerous, transverse striations, like the striped mus-
cles of vertebrates.

Make a figure of a muscular fiber.

In this outline each series or layer of closely parallel
fibers is considered as a separate muscle rather than an
aggregation of muscles. It complicates the subject unduly
to consider each distinct fiber a distinct muscle as has been
done by some writers. Thus Lyonet in his " Traite Ana-
tomique de la Chenille, que range le bois de saule " describes
1,647 muscles without including the muscles contained in the
viscera or those contained in the head.

Take a larva of Corydalis, which has been opened on the
ventral side and from which the alimentary canal and the

53

larger masses of fat have been removed, and study the ental
layer of muscles of the dorsal wall of the abdomen.

On each side of the heart and ectad of the wings of the
heart, there are great bands of longitudinal muscles, occupy-
ing the space between the heart and the prominent muscles
that extend dorso-ventrad on the sides of the body. Of the
longitudinal, dorsal muscles there are two sets on each side.
The wider set, which lies near the heart, may be termed the
great-dorsal-recti-muscles ; the narrower set, which lies be-
tween the great-dorsal-recti-muscles and the dorso-ventral
muscles of the sides of the body, may be termed the small-
dor sal-rccti-muscles.

Of the dorso-ventral muscles of the sides of the body, re-
ferred to above, there are two large bundles on each side of
each segment they are situated near the union of the seg-
ments.

Between the lateral muscles and the cut edge of the speci-
men (the dorsimeson) lie the great- ventral- recti- imtscles.
These differ from the great-dorsal-recti-muscles in being
somewhat oblique (this is shown better in specimens opened
on the back).

Make a drawing of the third, fourth, and fifth abdominal
segments representing the muscles mentioned above.

Carefully remove the recti muscles in one or two abdomi-
nal segments and note that ectad of them are many muscles
extending obliquely in various directions. The study of
these oblique muscles will be omitted in this course.

CHAPTER IV.

ANATOMY OF THE LARVA OF THE GIANT CRANE-FLY
(HOLORUSIA RUBIGINOSA).

As the larvre of Corydalis are not to be found on the
Pacific Coast (and in some other parts of the United States)
an account of the anatomy of the larva of a crane-fly (Tipu-
lidge) is presented for the use of students who may not be
able to work with Corydalis. The largest Tipulid is the
Giant Crane-fly, Holontsia rubiginosa, found commonly on
the Pacific Coast. The larvae of this Tipulid attain a length
of two to two and one-half inches, and by the absence of fat
in the body-cavity, and the ease with which they may be
perfectly preserved and readily dissected offer especially
available subjects for the study of the internal insect anat-
omy. As Holorusia does not occur elsewhere in the United
States than on the Pacific Coast (as far as is known) students
in other regions (in which Corydalis also does not occur) will
have to use the larva of some other Tipulid species. Some
rather large Tipulid is common in almost every locality.
The account of Holorusia will be found to answer as a guide
to the dissection of any other Tipulid larva.

EXTERNAL ANATOMY.

Technical note. — Bring a number of the larvae of Holo-
rusia (or other large Tipulid species, to be found in wet
moss, vegetable slime or about grass roots in pastures, etc.)
alive into the laboratory. Note the various motions and the

54

55

locomotion of the body. Kill specimens by dropping into
boiling water. After the specimens have straightened out
and stiffened, requiring about a minute (death is almost in-
stantaneous) remove to thirty per cent, alcohol. After two
or three hours remove to fifty per cent, alcohol, and after
three hours into seventy per cent, alcohol. After twelve to
twenty-four hours remove the specimens to eighty-five per
cent, alcohol, in which keep them.

Structure of body. — (Verify the following statements if
Holorusia is used : if another Tipulid is used compare con-
ditions with those here described.) The body is composed
of thirteen segments (exclusive of the head). Retracted into
the (apparently) first and second segments is the head, with
strongly chitinized skull. At the anterior end of the head,
usually projecting slightly, are the short, cylindrical, unseg-
niented antenna and the strongly chitinized month-parts.
{The mouth-parts can be better examined after the larva
has been dissected and the retracted head wholly exposed.)

There are no legs or tracheal gills (as there are in the larva
of Corydalis). The hindmost body-segment bears terminally
on a flat surface two large spiracles (breathing openings, see
p. 74, Comstock's Manual), surrounded by six backward pro-
jecting flexible lobes. On the ventral surface of this seg-
ment is the anal opening of the alimentary canal on an eleva-
tion bearing four large and two smaller flexible processes.
The segments of the hinder half of the body have each a
median transverse constriction ; those of the anterior half
are difficult to distinguish from one another but it is as-
sumed that each pair of the lateral groups of seta of which
five pairs may be noted, represents a segment. The ab-
sence of all paired appendages back of the head is to be
noted.

Make a drawing of the whole oody of the larva from a lat-
eral aspect.

INTERNAL ANATOMY.

Technical note. — With fine scissors cut open the body
along the median line of the dorsum, cutting through only
the body-wall. Put the specimen in a dissecting * dish, pin
out the cut edges with ribbon pins and cover with water.

Adipose tissue. — The most conspicuous organ in the
opened body-cavity is the alimentary canal extending as a
long thick tube longitudinally from head to caudal extremity.
It is nearly entirely enclosed in a thin, whitish, perforated
sheet of adipose tissue, or fat. Note the disposition of this
sheet. Examine a small piece in water on a slide under the
microscope, first under low power and then under higher
power. Make a drawing showing the structure of adipose
tissue as thus shown.

Alimentary canal and accessory parts. — The aliment-
ary canal is composed of a series of successive regions or
parts ; first (foremost) the slender oesophagus, embraced by
the circumxsophageal nerve commissures with the small white
brain lobes above ; second, an abruptly dilated conical part,
\\\z proventriculus ; third, a part immediately behind this and
not sharply marked off from it, the elongated ventriculus
bearing at its anterior end four elongated pouches, the gas-
tric cxca. In the sheet of adipose tissue surrounding the
ventriculus several slender convoluted thread-like processes
may be seen ; these are the Malpighian tubules, the organs of
excretion, four in number. They arise from the alimentary
canal just back of the ventriculus at a part marked by a pale
transverse line. Behind this line is a fourth part of the ali-
mentary canal, the small intestine. It is of smaller caliber
than the ventriculus and opens into a succeeding part of the
canal, the large intestine, near its anterior end. The large m-

* For directions for making dissecting dish see pp. 34-35.

57

testine is largest in front and tapers posteriorly to the very
narrow hinder part which is called the rectum. That portion
of the large intestine in front of the point of entrance of the
small intestine may be called the intestinal c&c inn.

For an account of the functions of the different parts of
the alimentary canal see the Cambridge Natural History,
Vol. V., pp. 123-127.

Salivary glands. — The salivary glands lie one on each
side of the oesophagus. Each is a white, firm U-shaped body,
with the two arms much thickened, and the inner reaching
a little farther forward than the outer. The salivary duct
arises from the outer lobe ; the two ducts run forward and
unite beneath the oesophagus, the common duct thus formed
opening into the mouth-cavity.

Without removing the alimentary canal, make a drawing
of it and the salivary glands in position in the body.

Examine a piece of salivary duct in water or glycerine on
a slide under the microscope. Note the transversely striated
condition. Remove the cover-glass and with needles pull
the duct gently apart. Examine again ; the two parts will
probably be connected by a spiral thread ; this will be
seen to be what formed the transverse striation ; it is really
a spiral thickening of the walls, not in a continuous thread,
but in a series of short, independent spirals of one or few
turns, called tcenidia.

The respiratory system. — The external openings, spir-
acles, of the respiratory organs, have already been noted in
the examination of the external parts of the specimen. Each
of these two spiracles opens internally into a main air tube,
trachea, which runs forward through the whole length of the
body. In each of the segments, from the fourth to the tenth
inclusive (not counting the head), a large branch trachea is
given off from the main longitudinal trunk to the alimentary
canal, and a smaller one to the dorsal blood-vessel (see postea).

58

Make a drawing of the tracheal system, tracing the longi-
tudinal and lateral vessels as far as possible.

Cut off a small piece of one of the lateral tracheae and ex-
amine it in water or glycerine on a slide under the micro-
scope. Note the tubular character of the trachea, and note
the five transverse striations clue to spiral thickenings of the
inner wall of the vessel. Pull apart pieces of trachea to show
the tanidia. See p. 47. Make a drawing of a piece of
trachea to show its structure.

For an account of the respiration of insects, see the Cam-
bridge Natural History, Vol. V., pp. 128-132.

The reproductive organs. — The reproductive organs
consist in the male of two small, white oval bodies, the testes,
lying one on each side of the large intestine imbedded in the
muscles of the tenth body-segment, and of a delicate duct,
the vas deferens, running posteriorly from each to the ventral
wall of the penultimate segment. In female specimens the
white bodies, ovaries, are larger and more elongate than the
testes of the male, and the oviducts (corresponding to the vasa
deferentia) are more easily seen.

Make a combined drawing showing the alimentary canal,
salivary glands, tracheal trunks, and reproductive organs in

£j

position in the body.

For a dissection of the reproductive organs in an adult
insect, see pp. 41-46.

The nervous system. — Remove the alimentary canal,
cutting across the oesophagus near the anterior end of the pro-
ventriculus. The£ra/« is composed of two main lobes united
posteriorly and lying above the oesophagus. Beneath the brain,
just under the oesophagus, lies the sub&'sophageal ganglion,
which is connected with the anterior end of the brain-lobes by
the circumtKSophagfal commissures, nerve-cords which together
with the brain and suboesophageal ganglion form a complete
ring around the oesophagus. Back of the suboesophageal

59

ganglion is a chain of four closely connected ganglia. Lead-
ing back from the hindmost of these ganglia are paired, but
closely opposed, longitudinal nerve-cords. On these cords
in the sixth body-segment is another ganglion, and following
this are five others similar to it, each lying over the center of
the sternal part of a segment. These ventral ganglia, from
the subcesophageal back, and the connecting longitudinal
commissures constitute the ventral nerve chain which with the
brain and circumoesophageal ganglia compose the central
nervous system of the insect. In addition to this central sys-
tem there is another smaller system, the sympathetic nervous
system, which we shall not study in this elementary dissection.
Each ganglion of the ventral chain, behind the suboesophageal
ganglion, gives off four very conspicuous nerves; one on
each side arising from the middle of the ganglion going to
the muscles of the body-wall, and another arising from the
anterior end of the ganglion going to the viscera. The 1'ast
ganglion lying in the antepenultimate body-segment, in ad-
dition to the four lateral trunks, gives off from its posterior
part two large divergent ones running backwards to the two
following segments. The brain and subcesophageal ganglion
give off nerves to the organs of the head.

Make a drawing of the nervous system.

The muscular system. — Along each side of the dorsal
and ventral median line of the body is a wide band of longi-
tudinal muscles. The most conspicuous fibers reach from
the anterior to the posterior border of each segment, but the
others reach from either end to the middle, while others ex-
tend from the middle of one segment to the middle of the
preceding or following segment, while still others are attached
to various points of the body-wall between the attachments
of the sets already mentioned. Finally, there is an inner-
most set of lateral transverse muscles in the anterior half of
each segment.

6o

Make a drawing showing the complete musculation of two
successive segments.

The circulatory system. — Cut a second specimen open
longitudinally along the median line of the venter, reserving
the first specimen for some later work. Pin out the cut
edges. Note again the general disposition of the body or-
gans so far examined. Examine again the reproductive or-
gans ; the specimen may be of the other sex from that pre-
viously studied. Remove the alimentary canal.

The dorsal vessel or heart is a slender, delicate, membranous
tube composed of a number of successive parts or chambers
lying along the median line of the back. To see this well
cut out the median dorsal strip of body-wall carrying the
heart and transfer it to a glass slide. Cover with water and
examine first under the simple microscope and then under
the low power of the compound microscope. It will be dis-
tinctly seen that toward the middle of each segment from
the last to the third inclusive, the tube becomes dilated,
forming a chamber, and in most of these chambers, except
the last, a pair of internal valves may be seen. From the
most anterior chamber a straight, tapering tube, the aorta,
runs forward into the head, where it ends by dividing into
branches which can be followed for but a short distance, ap-
parently fading out completely. There are no other blood-
vessels in the body.

On each side of each chamber may be noted a fan-shaped
group of very delicate muscle fibers, apparently attached to
the sides of the chamber, and called the wing muscles of the
heart. The convergent outer ends of these muscles are at-
tached to the body-wall on the line of the median constric-
tion in each segment. These muscles really lie in a thin
membrane which forms a sort of pericardia! membrane enclos-
ing a sinus on each side of the heart and stretching across
from these lateral sinuses to the body- wall as a septum or

6i

diaphragm. This membrane is attached to the heart on its
dprsal and its ventral surface. The membrane and sinuses
can be especially well seen in cross sections of the body.

For an account of the circulation in insects see the Cam-
bridge Natural History, Vol. V., pp. 132-136.

The histoblasts of wings and legs. — Returning to the
first specimen (that opened along the dorsum) carefully re-
move the muscle fibers from the body-wall of the three front
(thoracic) segments of the body, not including the head. Be
careful not to remove certain small whitish bud-like bodies
lying between the muscles and the body-wall. In specimens of
sufficient age the histoblasts (or imaginal buds or imaginal discs
as variously called) of the wings and legs of the adult fly and
of the external prothoracic respiratory tubes may be seen as
small sac- or bud-like bodies lying against and attached to
the inner surface of the body-wall of the thoracic segments.
There are two pairs of these imaginal buds in each thoracic
segment corresponding respectively to the prothoracic legs
of the imago and prothoracic respiratory tubes of the pupa,
the meso-thoracic legs and wings of the imago, and the meta-
thoracic legs and halteres of the imago. The study of the
morphology and development of these imaginal buds is too
difficult to be referred to here. It is sufficient to know that
the legs and wings of the fly begin thus to develop under the
surface of the body and continue this internal development
until the larva changes into a pupa. These buds may be
seen to be intimately connected with the thoracic skin, and
are, in fact, actual invaginated parts of this skin.

The head and its appendages. — After finishing the dis-
section of the internal organs remove the head entirely from
the rest of the specimen and examine with simple microscope.
Each of the short antenna arises from a small lobe on the plate
covering the top of the head. This plate is long, tapering and
decurved behind. It is united along the anterior parts of its

62

sides with lateral plates, while the anterior margin is re-
entrant receiving the smaller end of the pear-shaped labrum.
The distal part of this sclerite is membranous except for two
lateral chitinizations. Posteriorly it is fused with the epicra-
nial plate. The lateral plates are each oval and shell-shaped,
having their anterior lower angles produced forward and
united with each other. The single process thus formed pro-
jects forward and curves upward between the faces of the
posterior jaws. The tips are provided with graduated teeth.
In front of each lateral plate is a narrow dorso-ventral scle-
rite carrying the jaws. The anterior ones, mandibles, are
large, strong, toothed terminally and provided on the inner
side with a large, softer, movable lobe. The posterior jaws,
maxilla;, are less strongly chitinized than the mandibles.
They are flat, and each is provided at its outer angle with
several papilla-like processes.

CHAPTER V.

THE EXTERNAL ANATOMY OF A BEETLE.
Pterostichus calif ornicus.

With the knowledge of the external anatomy of the locust
as a basis the student may successfully attempt to examine
comparatively some of the various conditions of the body
exhibited among different orders of insects. With the varied
habits of insects there are necessarily correlated various
modifications of structure, internal and external. The modi-
fications of the external structure are those taken special
cognizance of and used in the present analytical tables and
keys for insect classification, and must be studied to some
degree before determination of insect forms can be done in-
telligently. The study of insect anatomy in a comparative
way will also give the student an understanding of the sig-
nificance of homology and specialization.

As an example of simple work of this character which
may be undertaken by the student, the external anatomy of
a beetle (order Coleoptera) may be studied.

The peculiarly flattened form of many insects, by which
the lateral aspects of thorax and abdomen are reduced to a
mere ridge or margin, is accompanied by a change in the
position of many of the body sclerites, in particular the
pleural sclerites of the thorax. This condition is well ex-
emplified among the predaceous ground-beetles (Carabida)
and almost any species may be selected for illustration. We
have chosen the species Pterostichus calif ornicus, as the repre-
sentative of a widely spread genus, and the description fol-

63

64

lowing applies especially to this form ; however, the notes
will serve as a guide for the examination of any member of
the genus.

The meso- and metathoracic segments are closely joined
to each other and to the abdomen. The prothorax is freely
movable and is constricted at its articulation with the meso-
thorax, so that it appears to form all of the second or tho-
racic region of the body. The insertion of the hinder two
pairs of legs, however, shows that part of what at first
glance appears to belong entirely to the abdominal region of
the body really belongs to the thorax. The body-wall is
very strongly chitinized, the body being enclosed in a veri-
table coat of armor. The head projects horizontally f-rom
the body instead of hanging vertically across the front, as
with the locust, and the flattening of the body is evident in
all regions, head, thorax, and abdomen.

PARTS OF THE HEAD.
THE FIXED PARTS OF THE HEAD.

The fixed * parts of the head are fused so as to form a
strong and rigid box, which is elongated and flattened.

Epicranium. — The epicranium bears on its cephalic por-
tion two impressed lines which run cephalad until they meet
the transversal clypeal suture, the suture separating the cly-
peus from the epicranium. f Laterad of each of the impressed
lines on the epicranium there is, forming the dorso-lateral
margin of the head, a sharp ridge called the frontal ridge,
which runs cephalad from the dorsal margin of the eye.

"The "head-capsule" of this beetle is very strongly chitinized and deep
black in color. To soften and partly bleach the head, so that the fixed parts
may be readily determined, the student must boil the head for some time in
caustic potash (KOH).

tThe epicranium of the beetle, like that of the locust, is a compound sclerite,
being composed of the fused true epicranium and front.

65

The antennae arise just below this frontal ridge in a short,
rounding groove running cephalad from the eye. On the
epicranium just above each compound eye are two, long
hairs arising from distinct pits. These pits are called setiger-
ous punctures. Similar punctures and hairs are found also
near the lateral margins of the clypeus.

Clypeus. — The clypeus is broader than long, and projects
cephalad between the bases of the mandibles. Projecting
cephalad from the cephalic margin of the clypeus, is the sub-
quadrangular labrum, with its distal margin slightly concave
outwardly.

Compound eyes. — The compound eyes, on the lateral mar-
gins of the head, are comparatively small.
Ocelli. — There are no ocelli.

Genae. — The portions of the epicranium below the eyes
and antenna; are the genes and each projects cephalad, latero-
ventrad of the base of the mandibles, as a thin tapering
tongue curving inward slightly at its tip. Below this pro-
jecting process, the gena presents a rounded emargination,
and, filling in the emargination, may be seen the basal por-
tion of the maxillae. The genae form, with portions of the
occiput, the lateral portions of the ventral surface of the
head.

Occiput. — The occiput, although fused with the epicra-
nium to form the firm head-box, is plainly separated from the
epicranium on the dorsal and lateral portions of the head by
an impressed line, which fades out on the lateral portions of
the ventral surface of the head, so that the postgenal and
occipital regions cannot here be distinguished.

Gula. — Forming the mesal third of the ventral aspect of
the head, slightly widening caudad, and expanding at its
cephalic extremity to a narrow, transversal bar, which pro-
jects laterad to the genal emargination, is the gnla, one of
the head sclerites, which is wanting or is fused with the sub-

66

mentum in the head of the locust. The gula is usually a
well developed sclerite among beetles. The sutures separat-
ing it on either side from the contiguous portions of occiput
and epicranium (postgena) are called the gular sutures.

Make a drawing of the ventral aspect of the head, show-
ing the skeletal parts described, and also what may be seen
of the mouth-parts /// situ.

THE APPENDAGES OF THE HEAD.

Antennae. — The antenna, are filiform, and i i-segmented ;
the third segment is the longest one. The proximal three
segments are glabrous, and the second and third bear each
two or three longish hairs near their distal end. The re-
maining eight segments are finely pubescent. In addition
each of these eight bears a few longer hairs at its distal end.

Mouth-Parts.

The mouth-parts are fitted for biting and are in general
similar to the mouth-parts of the locust.

Labrum. — The labrum has been described already as a
part of the skull.

Mandibles. — The mandibles are rather long, and taper
distad to a sharp, curving tooth. They bear on their sharp,
cutting, inner margin, near the base, a few, small, blunt
teeth, and their outer face presents a broad, shallow groove
or furrow called the mandibular scrobe. Make a drawing cf a
mandible.

Maxillse. — The maxilla, differ especially from those of
the locust by the presence of an additional sclerite, the sub-
galea, by the side of the stipes, as if the stipes were divided
by a longitudinal suture. The cardo is large, and broadly
club-shaped ; the median portion of the maxilla is composed
of three sclerites, the stipes, palpifer and subgalea. These

67

three sclerites may be distinguished when the maxilla is
viewed from the dorsal aspect by the following characters ;
the palpifer lies above the distal two-thirds of the stipes,
and also overlaps part of the subgalea. It is elongate, sub-
triangular in outline with apex directed toward the lacinia.
From it arises the four-segmented palpus, and it also bears
near the origin of the palpus a single, conspicuous, long
bristle. The stipes as seen from above is elongate and
rather slender, with the basal extremity widened. It lies
laterad of the large subgalea, which forms the inner or mesal
half of the median portion of the maxilla. From the sub-
galea the two lobes, galea and lacinia, of the maxilla arise.
The galea is slender, elongate, distinctly two-segmented, and
palpiform in character. The lacinia is strongly chitinized,
and is beset on its inner face with strong and long, curved
spines, and on its dorsal aspect with many, weaker hairs.
It bears on its distal end a strong tooth or curved tip, known
as the digitus.

Make a drawing of the dorsal aspect of a maxilla.

Labium. — The lalrium is separated from the cepnalic
transverse portion of the gula by a straight, transverse
suture. The snbmentum is large, strongly chitinized, and
with its lateral portions appearing as broad, expanded lobes,
separated by a broad and deep, cephalic emargination.
Bordering this emargination is the narrow curving mentitm,
with a median forward-projecting, two-pointed portion.
From the elongated, subcylindrical, forward-projecting pal-
pigers arise the three-segmented labial palpi, the first seg-
ments of which are very short. Also projecting forward
from the mentum is the ligula, composed of a dorsal or
inner, delicate, transparent, membranous part, which divides
at its tip into two, slender, tapering projections, the para-
glossce, and a ventral or outer, chitinized, undivided portion,
\hzglossa. The tip of the glossa is truncate, and bears two,

68

long, strong hairs. Each paraglossa lies slightly laterad of
the distal half of the glossa. The entire ligula arises, not
from the cephalic margin of the mentum, but from its inner
or dorsal face, and it may be that its parts are not homolo-
gous with the terminal lobe (ligula) of the locust's labium,
but that one or perhaps both parts are continuous with the
lining of the mouth-cavity ; in which case they would be
homologous with the hypopharynx of the locust's mouth.

Make a drawing of the ventral (outer) aspect of the
labium.

PARTS OF THE THORAX.
PROTHORAX.

Dorsal aspect. — T\\t pronotum is not divided into differ-
ent sclerites, but appears as a single, firm, convex plate, bear-
ing a median impressed line, and, laterad of this line, on
each side near the caudal margin, a short, linear depression.
At the acute lateral margins, the pronotum is in flexed,
extending a little distance ventro-mesad on the ventral
(pleural s. sfr.} aspect of the body. This inflexed portion is
often called the prothoracic epipleura.

Ventral aspect. — The sternum and the true pleural scle-
rites or " side pieces," together form the ventral aspect of
the prothorax.

Sternum. — The sternum, constituting the median region of
this aspect, is irregularly saddle-shaped, with a caudad-pro-
jecting tongue between the coxal cavities. This tongue after
reaching the caudal margins of the coxte bends at right
angles and projects dorsad, the end expanding slightly into
two dorso-laterad projecting points, which meet a ventro-
mesad projecting point of the epimeron on each side, and thus
form part of the enclosing, caudal boundaries of the coxal
cavities.

69

Episternum, — The episternum, a large rhomboidal sclerite,
constitutes most of the body-wall between the sternum and
the epipleurae.

Epimeron. — Separated from the caudal extremity of the
episternum by a distinct suture, is the narrow, curving
epimeron, whose expanded mesal extremity presents two,
pointed, curving processes, which enclose the coxal cavity
laterad and caudad. The meeting of the epimeron and
sternum caudad of the coxal cavity technically closes it, or
makes it entire ; if these two sclerites do not meet, as is
often the case among beetles, and the cavity is bounded
caudad simply by membrane, the cavity is said to be open.
If there is no caudal tongue projecting between the cavities,
they are said to be confluent ; when separated, as in the speci-
men in hand, by this tongue, they are technically separate.

MESOTHORAX.

Dorsal aspect. — When the wing-covers are folded the
only part of the mesonotum visible is the small, median, tri-
angular or shield - shaped portion of the scutellum. By
spreading apart or breaking away the wing-covers, the lat-
eral membranous portions of the scutellum may be seen, as
well as the scutum ; the median part of the scutum is
strongly chitinized and the lateral parts, weakly chitinized.
The postscutellum also may be distinguished as a narrow,
weakly-chitinized, curving bar, running laterad on each side
just in front of the caudal apex of the scutellum. The
prcescutum is represented merely by a thin, transversal strip
of membrane.

Ventral aspect. — As with the prothorax the ventral
aspect of this segment is composed of the sternum and the
pleural sclerites.

Mesosternum.— The mesostermtni is plainly set off by
sutures. Its caudal margin has a broad, median tongue,

;o

which projects caudad between the coxal cavities, and is
angularly emarginated at its tip. Laterad of this tongue are
two rounding emarginations, for the reception of the coxae.
Bounding each coxal cavity laterad is a caudad-projecting
portion of the sternum. Cephalad the sternal sclerite tapers
somewhat, and the cephalic margin is narrowly truncate.
A narrow, collar- like cephalic margin which fits into the pro-
thorax, is separated from the rest of the sternum by a slight
carina or elevated line.

Episternum. — The pleural sclerites are distinct ; the epi-
sternuin is large, angularly concave, and does not reach the
coxa. It bears near its cephalic margin two, transversal
raised lines or carinae, one of which is a continuation of .the
collar-making carina of the sternum. Like the sternum, the
cephalic margin of the episternum fits into the prothorax.
The lateral margin is angularly inflexed along its entire
length, as is the case with all the pleural sclerites. The
narrow, inflexed portion is covered when the wing-covers
are closed by the inflexed, lateral margin of the wing-
covers.

Epimeron. — The epimeton, lying along the caudal margin
of the episternum, is a narrow, transversal sclerite. Its
mesal extremity docs not reach the coxal cavity, but lies
contiguous to the lateral margin of the metasternum.

METATHORAX.

Dorsal aspect. — When the elytra are closed the meta-
notum is completely covered and invisible. By removal of
the elytra, the metanotum is revealed as a narrow transver-
sal bar, on the surface of which a number of sutures and
elevated and depressed lines are to be seen. The work of
distinguishing the various component sclerites of the meta-
notum cannot be done satisfactorily by the elementary
student. There is a conspicuous depression or groove ex-

tending caudo-cephalad along the middle of the back, with
strongly chitinized margins which project slightly mesad
over the depression. On the inner surface of the elytra,
near the base of the mesal margins, there are two, slight,
projecting processes. These small processes have strong,
acute margins, which project slightly laterad. When the
elytra are closed, the raised processes fit into the groove of
the metanotum, and the laterad-projecting margins of the
processes lie under the mesad ^projecting margins of the
groove, the whole structure forming a means for the firm
holding of the elytra over the dorsum of the body. The
firm holding of the elytra is further aided by the inflexed
lateral margins and by the close dovetailing of the mesal
margins along the middle of the back.

Ventral aspect. — As in the other thoracic segments this
includes both the sternum and the pleural sclerites.

Metastermun. — The metasternum is, as the mesosternum,
best described as saddle-shaped. It has a rather broad,
blunt tongue, projecting cephalad between the mesocoxae to
meet the caudad-projecting tongue of the mesosternum. It
presents, also, an acute-angle process, projecting caudad
between the cephalic halves of the metacoxse. The "sad-
dle-flaps," or lateral lobes of the metasternum expand later-
ad, and their cephalic margins, concavely rounded, form the
caudal boundaries of the mesocoxal cavities. There is a
line or suture running transversely across the metasternum
near the caudal margin which does not reach the lateral
margins. That portion of the metasternum caudad of this
suture is called the antecoxal piece of the metasternum.

Episternum. — The rhomboidal episternum is the largest of
the pleural sclerites.

Epimeron. — The trapezoidal epimeron, though smaller than
the episternum, is broader, and more conspicuous than that
of either of the other thoracic segments.

72

Make a drawing of the ventral aspect of the entire thorax,
including the legs of the left side.

APPENDAGES OF THE THORAX.

The hind wings are wanting in this beetle. This is ex-
ceptional, however, among beetles, the hind wings, mem-
branous and with a few strong veins, being usually well-
developed, and differing from the wings of most insects in
being folded transversely as well as longitudinally when the
insect is at rest.

The fore-wings are very strongly chitinized and thick-
ened, and are called elytra or wing-covers. When the beetle
is at rest the elytra fit closely over the dorsal aspect of the
meso- and metathorax and abdomen, protecting the abdo-
men and hind wings, which (when present, as in most bee-
tles) lie folded over the metathorax and abdomen and
beneath the wing-covers. The elytra are articulated with
the body so as to be freely movable, being outspread when
the beetle is in flight. The basal or articulating parts of
the elytra lie just ventro-laterad of the lateral margins of
the scutellum. The expanded flap or wing-like parts pre-
sent a series of sub-parallel, longitudinal, impressed lines,
and the lateral margins, termed epipleurcz, are inflexed over
the dorso-latera] margins of the body. This inflexed con-
dition of the margins does not extend quite to the tips of
the elytra, but disappears at a point where the margin ap-
pears to be interrupted. On the inner surface of each ely-
tron near the lateral margin there is a distinct longitudinal
fold or plica,

PARTS OF THE ABDOMEN.

The abdomen is composed of a number of very much
flattened segments ; and its dorsal surface or tergum is com-
pletely covered by the elytra when they are closed. On the

73

ventral surface, six strongly-chitinized sterna may be count-
ed. The first (basal) sternum is completely divided by the
coxal cavities, so that it appears as two triangular pieces,
lying laterad of the coxse. The cephalic margin of the sec-
ond sternum is emarginated on each side of the meson by
the coxal cavities, so that the mesal part of the cephalic
margin appears as an acute, cephalad-projecting process.
The third, fourth and fifth sterna are of about equal length
(caudo-cephalic), the sixth being longer and having its cau-
dal margin roundly pointed. The first, second and third
sterna are connate (firmly united, not movable on each
other), although the sutural lines are distinct. All of the
sterna have strongly chitinized, lateral margins, which pro-
ject somewhat dorsad, and then are narrowly inflexed over
the dorso-lateral margin of the abdomen. There are seven
terga, the tergal aspect corresponding to the sixth sternum
being unequally divided by a transversal suture, producing
thus an additional small tergum. All of the terga are mem-
branous except the sixth and seventh, which are chitinized,
and are known respectively as the propygidium and pygidium.
The propygidium is coarsely punctulated, but the surface of
the pygidium is smooth. Each tergum except the seventh
bears a pair of spiracles, located near the cephalo-lateral
angles of the terga. Between the lip-like caudal margin of
the pygidium and the sixth sternum there is a transversal
fissure, in which lie the anal and genital openings.

CHAPTER VI.
THE MOUTH-PARTS OF INSECTS.

The study of the mouth-parts of insects is of special in-
terest and importance because of the admirable illustration
of the principle of homology presented by the mouth-parts,
because in the classification of insects great importance is
assigned to the mouth-structure, and finally because of .the
significance of the structural character of the mouth in the
study of the habits and economic relations of insects.

The mouth-parts of the locust, the cockroach, and the
beetle have already been studied: they represent the biting
type of insectean mouth-parts. The student is, therefore,
already acquainted with the component parts of the mouth,
and with their character in the biting type. The mouth-
parts of many insects, however, are not of the strictly biting
type, but are modified to form an elongate tubular beak or
proboscis used for sucking liquid food, or are modified to
form a combination of the biting and sucking types. This
modification of the more generalized biting type varies in
the various insect orders possessing "sucking mouth-parts."
As a beginning in the comparative study of the sucking type,
the mouth-parts of a short series of insects, representing sev-
eral important orders, may be examined.

In the examination of the mouth-parts dried specimens can
be advantageously employed. Remove the head from the
dried insect and boil it in dilute potassium hydrate (KOH) to
soften and partially bleach the chitinous parts. The length
of time of boiling will depend, of course, upon the degree of

74

75

chitinization and coloration of the parts. The head should
then be washed in water and removed to a watch glass con-
taining water. The mouth-parts can now be examined in situ
and finally readily dissected apart by means of dissecting
needles and forceps.

The parts can be temporarily mounted in glycerine, or if
permanent mounts are desired, the parts can be mounted in
glycerine jelly. Carry from the water directly into the jelly.
For mounting in Canada balsam the parts must be thoroughly
dehydrated by carrying through successive strengths of alco-
hol up to absolute, and then clearing in xylol or other clear-
ing oil.

BITING AND SUCKING MOUTH-PARTS.

In the Hymenoptera, the mandibles retain their function
of biting, while the maxillae and labium unite to form an ap-
paratus for lapping or sucking liquids. Two examples of
this condition of mouth-parts fitted for biting and sucking
may be examined : a wasp, in which the maxillae and labium
are somewhat elongated and fitted for lapping ; and a honey-
bee, in which the maxillae and labium are much elongated
and fitted for sucking.

MOUTH-PARTS OF THE WHITE-FACED HORNET.

Vespa maculata ; order Hymenoptera.

Because of the considerable membranous and fleshy tissue
of the mouth-parts, bleaching in KOH should not be carried
far ; a minute or two of boiling, sufficient for softening, will
do. In fact, simply softening in warm water is perhaps safer.

The mouth-parts of the wasps and bees are so thoroughly
united at the base by the development of the pharyngeal
skeleton and membrane that a considerable tearing of tissue
is necessary to separate the parts. The mouth-structure as

76

a whole should be carefully examined before the parts are
dissected out.

In the study of the mouth-parts of insects the student
should bear in mind that the labrum, although in position
and use actually one of the mouth-parts, differs morphologic-
ally from the mandibles, maxillae and labium in not being a
modified pair of head appendages.

Labrum. — The labrum is short and broad, and is immov-
ably fused with the clypeus.

Epipharynx. — Directly underneath the labrum is the well-
developed elongate strap-like epipharynx. It is fleshy and
membranous and bears numerous, spiny hairs.

Mandibles. — The mandibles are large and toothed. When
they are closed one overlaps the other to a considerable
extent.

Maxillse. — The maxillae, although of the generally simple
character of the biting type, show some rather confusing
modifications. The cardo is strongly chitinized, distinct,
rather large and subclavate in shape. The stipes is large,
strongly chitinized and is (like the stipes of the beetle's
maxilla) partly divided into three sclerites, from one of which
rises the small, slender, six-segmented palpus. The terminal
lobes assume a peculiar character, the distinctly two-seg-
mented galea being large and flat, and bearing many papillar
hairs. From the large basal segment of the galea there rises
a distinct, flattish lobe also bearing many long papillar hairs.
Make a drawing of a maxilla.

Labium. — The labium is a complex organ in which, how-
ever, the typical composing parts can be pretty readily dis-
tinguished. The submentum and mentum are fused to form
a large strongly chitinized, bent, basal sclerite. This scle-
rite is bent so as to present a strongly convex under (outer)
surface, and a deeply concave upper (inner) surface. This
deep concavity or furrow is filled, with the fleshy and mem-

77

branous folds of the hypopharyngeal or ventral lining of the
mouth. There is a certain, short, broad, fleshy flap which
may be called the hypopharynx. From this basal sclerite
(fused submentum and mentum) arise the slender four-seg-
mented labial palpi, and the terminal lobes. The paraglossae
are distinct, thin, membranous structures with the basal por-
tion well chitinized and with a peculiar button-like chitinized
tip. The glossae are fused at their base, and show a well-
developed basal chitinous skeleton-plate. The membranous
portions of the glossae are also fused for about half their dis-
tance ; the apical halves, however, are free, and each one
bears a button-like, chitinized tip, like the tips of the para-
glossae.

Make a drawing of the labium.

Make a drawing of the cephalic aspect of the head showing
the fixed and movable parts.

MOUTH-PARTS OF THE HONEY-BEE.

Apis nielli fica ; order Hymenoptera.

Most of the bees in alcohol (if an alcohol specimen is
used) will be found to have certain of the mouth-parts pro-
truding.

These parts are the maxillae and labium, united at the base
and associated to form a sucking proboscis. Before the de-
tailed examination of these parts is begun the student should
discover the labrum and mandibles.

Labrum. — The labrum is small and oblong in shape with
its laterocephalic corners rounded. The breadth (lateral) is
about three times its length (caudo-cephalic).

Mandibles. — Partially concealed beneath the labrum are
the spoon-shaped mandibles. With forceps or needle, press
the mandibles apart at their tips (press laterad). Note that
the mandibles are not toothed, but are rather paddle or spoon-

78

like at the tips. Remove a mandible and make a drawing
of it.

Remove both mandibles and labrum, and grasp the re-
maining protruding parts with forceps and carefully pull
them loose from the head. Wash while still held in the for-
ceps, and mount in glycerine on a glass slide. Before reading
farther the student should endeavor to name the various
parts presented before him on the slide.

Make a drawing of the maxillae and labium, and name the
parts, tentatively. Compare the result with the notes fol-
lowing :—

Maxillae. — The parts of each maxilla present are the car-
do, stipes, galea (or lacina ; one of the two is probably want-
ing), maxillary palpi, and possibly the palpifer.

Cardo. — The carJo, or proximal part of the maxilla, is a
rather long, slender, strongly chitinized sclerite, somewhat
resembling a human femur or thigh-bone in shape. At its
proximal end it terminates in two unequal prongs, the point
of the larger being bluntly rounded. At its distal end
(articulating with the stipes) it expands club-like.

Stipes. — The stipes is an irregular, elongate sclerite, strongly
chitinized. Its proximal end is bluntly rounded and swollen.
The stipes articulates with the proximal segment of the galea
(see below) by a long diagonal face.

Galea. — The galea (we incline to believe this part homolo-
gous with the galea of the locust's maxilla, rather than with
the lacinia, because of its two-segmented condition) extends
distad from the stipes as a tapering blade-shaped piece. It
is composed of two segments. The proximal one is small
and triangular, articulating by the entire length of one of its
margins with the stipes. The distal segment or sclerite con-
stitutes the real blade-like portion of the maxilla, and nearly
equals in length the ligula and labial palpi (see below). Its
surface is unequally divided into two portions by a subme-

79

dian, dark-brown, longitudinal line. (This line may indicate
a coalescence of galea and lacinia into this one blade-like
compound sclerite.) This line bears several hairs, and there
are scattering hairs elsewhere on the sclerite, especially
toward the distal end. Near the proximal end of this distal
segment of the maxilla, and between the longitudinal line
and the outer margin, many two-jointed papillae (taste
organs ?) can be seen with a high power.

M' axillary palpi. — The maxillary palpi are minute, exarticu-
late, outward-projecting pieces, arising from near the outer
end of the suture separating the proximal from the distal
segment of the galea.

Labium. — The parts of the labium present are the sub-
mentum, mentum, glossa, paraglossse, palpifer, and palpi.

Siibmentum. — The sub mentum is a small, shield-like piece ;
its proximal end is connected by two chitinous bands, the
/onr, with the cardo of each maxilla ; its distal end articulates
with the mentum. The submentum is rather feebly chi-
tinized.

Mentum. — The mentum is rather oblong in shape, with
rounding corners, and strongly chitinized.

Glossa. — Rising from the distal end of the mentum is the
long glossa, which terminates in a small transparent lobe or
flabellum. The glossa should be carefully examined under
low and high magnification. Note the reticulated and hairy
surface. The visible surface is that of a sheath which en-
closes a slender flexible rod, the rod being probably con-
cerned with the movements of the organ.

Paraglossce. — At each side of the glossa, and rising from
near its proximal end are two subtransparent lobes or flaps,
extending about one-fifth the length of the glossa. These
are the paragloss?e.

Palpijers and Labial Palpi. — Lying just laterad of the para-
glossae and rising from the distal end of the mentum are

8o

two, long, flattened processes, composed of several segments.
The basal segment, which is the largest and longest of the
segments, extends forward for about one-half the length of
the ligula, and is the palpifer ; the succeeding three seg-
ments compose the labial palpus.

The proximal one of these segments is the largest and ap-
pears to be a direct continuation of the palpifer, separated
only by a narrow straight suture ; the remaining two seg-
ments are very small.

Make a drawing of the cephalic aspect of the head show-
ing the fixed and movable parts.

PIERCING AND SUCKING MOUTH-PARTS.

Among the insects whose mouth-parts are fitted exclu-
sively for piercing and sucking (or sucking alone) the man-
dibles, if present, are modified to form slender elongate sty-
lets or blades.

This is the condition presented by the Hemiptera, and
some of the Diptera ; with most of the Diptera and all of the
Lepidoptera (excepting Eriocephala) the mandibles are com-
pletely lost, or are so atrophied as to be functionless. As
examples of insects with strictly sucking mouth-parts the
student may examine a Cicada (Hemiptera), a horse-fly and
a house-fly (Diptera, one with and the other without mandi-
bles) and a butterfly (Lepidoptera).

MOUTH-PARTS OF A CICADA.

(Cicada sp.; order Hemiptera!)

The sucking beak, tapering from base to tip, will be
found, in dried specimens, usually appressed to the ventral
surface of the body of the Cicada.

Remove the head with the beak from the dried specimen,

8i

and examine the beak before dissection. The long, three-
jointed lalninn, forming all of the beak as seen superficially,
is specially chitinized (brown) near its distal end. The dis-
tal joint is the longest, and its surface is sparsely covered
with fine, whitish hairs. The tip is rather blunt than acute.
A narrow channel, widest at its proximal end, runs along the
upper face of the labium. In this channel, but concealed
by the approaching edges of it, lie the mandibles and max-
illae. A glimpse of the mandibles and maxillae just at the
base of the labium can often be had. Above the base of the
labium is the minute, acute-angled labrum lying just over
the entering mandibles and maxillae.

With a dissecting needle carefully break away the head-
wall and muscle near the base of the beak, especially dorsad
and laterad. The bases of the mandibles and maxilla will be
discovered as small, strongly chitinized (brown), terminal
dilations of slender, chitin rods, which run forward into the
channel of the labium. Note the relative position of the
two rods with dilated bases on either side, and decide which
is mandible and which maxilla. (The rod lying slightly
dorsad and laterad of the other is the mandible ; the man-
dible is also thicker and larger than the maxilla.) Trace the
slender chitin rods or stylets (the mandibles and maxillae)
into the channel of the labium. Here they are all closely
appressed, the two maxillae specially so, so that they can be
separated only with difficulty.

Remove the mandibular and maxillar stylets and note the
channel in which they naturally lie. The labium is more
strongly chitinized along the walls of the channel than else-
where, except at its tip.

Make a drawing of the mouth-parts from dorsal view,
with the mandibles and maxillae removed from the channel
of the labium and spread apart.

82

MOUTH-PARTS OF THE HORSE-FLY.

{Tabanus or Therioplectes sp.; order Diptera.)

Among the flies with piercing mouth-parts only the
females possess mandibles. It is therefore necessary to
select a female horse-fly (distinguished from the male by the
narrow space between the eyes ; in the males the eyes touch
each other for a greater or less distance along the dorsal
aspect of the head).

The projecting mouth-parts are conspicuous. On super-
ficial examination there may be noted two, thickened,
slightly curving, horn or club-like processes (the maxillary
palpi) projecting above a black, thickened stalk or trunk
(the labium), on the dorsal surface of which lie several light
brown, slender, pointed stylets (mandibles, maxillae, labrum,
epipharynx, and hypopharynx).

For the detailed examination of the mouth:parts, the head
of the fly should be removed from the body, a considerable
part of the head, laterad and caudad, broken away and the
remainder, with mouth-parts attached, boiled in KOH to
soften and bleach.

The large maxillary palpi are two-segmented ; the distal
segment is longer than the basal one, and compressed. The
proximal one is subcylindrical, and projects dorso-cephalad,
so that the large distal segment is carried above the rest of
the mouth-parts.

Lying along the dorsal surface of the large labial trunk
are six long, slender, pointed pieces or stylets. The upper-
most, unpaired, flat piece is the labrum (or perhaps labrum
and epipharynx fused). It is rather bluntly tipped and is
the broadest of the stylets. The flat, smooth, sharply
pointed mandibles lie just above the less strongly chitinized,
narrower, and finely marked maxilla. Corresponding some,
what to the labrum, but less broad and strong, is the sixth

83

stylet, an unpaired slender piece lying below the maxillse.
This is the greatly developed hypopharynx.* These six
stylets, labrum, mandibles, maxillae, and hypopharynx are
the instruments with which the female horse-fly pierces the
skin of animals to get at the blood ; the male has no pierc-
ing stylets, and feeds on flower-pollen.

Beneath the grouped stylets is the long trunk- or probos-
cis-like labium, presenting on its upper surface a shallow fur-
row in which the stylets may be partially enclosed, and pre-
senting at its distal extremity a conspicuous, expanded, disk-
like part called the label/a. This terminal disk is believed by
some entomologists to be composed of the greatly modified.
labial palpi. It is made up of two fleshy lobes or leaves,
bearing on the outer or under surface many fine, transversal,
subparallel lines or ridges. The two lobes can be closed
together like the leaves of a book.

Make a drawing showing all of the mouth-parts from the
dorsal view. The stylets can be spread apart laterad, so as
to expose the under ones.

In only a few families of Diptera are free mandibles pres-
ent, and when present they are possessed, as already men-
tioned, only by the females. In many flies there are no
piercing stylets, and as representative of these flies without
piercing mouth-parts the common house-fly may be studied.

MOUTH-PARTS OF THE HOUSE-FLY.

(Musca domestica ; order Dipteral)

In the house-fly the mandibular and maxillar stylets being
gone, we find only the trunk-like labium, with the labrum-
epipharynx lying closely appressed to, and almost fused with
its dorsal surface, and the maxillary palpi.

* The hypopharynx and the epipharynx (outgrowth from the upper wall of
the pharynx) are in most insects small, fleshy, and inconspicuous.

84

The maxillary palpi are prominent, but are only one-seg-
mented. The labial trunk or proboscis may be described as
being made up of three portions, a basal third, the basipro-
boscis, from which arise the maxillary palpi, and in which are
imbedded two slender chitinous rods, the "maxillary ten-
dons" probably representing the greatly reduced rnaxillas ; a
middle third, the mediproboscis, strongly chitinized ; and a
distal third, the distiproboscis, including the disk-like, fleshy
labella. The labella is like that of the horse-fly, but in the
house-fly it is the only organ for obtaining food. With it
traversed as it is by transverse, horny, chitinous ridges, the
" pseudotrachea" hard food substances may be rasped so that
fine particles of food mixed with, or sometimes dissolved in,
a salivary secretion, which issues from the ridges, can flow
into the mouth, along the dorsal furrow of the labial proboscis.

Make a drawing of the mouth-parts from a lateral view ;
and also of a portion of the labella, highly magnified, to
show disposition of the pseudotracheas.

MOUTH-PARTS OF THE MONARCH BUTTERFLY.

(Anosia plexippus ; order Lepidoptera?)

In the higher Lepidoptera the mouth-parts have under-
gone a profound modification ; mandibles are wholly want-
ing and the labium is reduced to a small, immovable sclerite,
not functional in food getting. The maxillce, on the other
hand, are greatly elongated and are united to form a long,
slender, coiling, sucking tube.

In examining the mouth-parts of Anosia it will be found
necessary to remove carefully the scales and scale-hairs
which cover the head before bleaching.

Labrum. — Immovably joined to the clypeus is a very
narrow, mostly transversal sclerite, the labrum. It bears two
tapering, cephalad- projecting points, the pilifers, rising from

85

the ends of the transverse portion of the sclerite. Each
pilifer bears on its inner margin a row of short bristly hairs,
light brown in color. There is also to be made out a very
small, triangular piece projecting cephalad from the middle of
the transverse portion of the labrum. This is the epipharynx.

Mandibles. — The mandibles are wanting in Anosia. (They
are present in an aborted condition in some Lepidoptera;
and in one genus of small moths, Eriocephala, are present
and functional, constituting, with the maxillae which are not
produced into a sucking tube, true biting mouth-parts.)

Maxillae. — The long, coiling, sucking tube of Anosia (as
of all the Lepidoptera possessing functional sucking mouth-
parts) is composed of the greatly extended, opposed, termi-
nal portions of the maxilla. In addition, there is a fixed
basal part of each maxilla, which cannot be divided into
tardo and stipes. This basal part, shining brown, extends
caudad and ventrad, partially bounding a cavity lying be-
tween it and the labium. The sucking tube consists of two
lateral portions, each portion representing a maxilla. These
parts are convex outwardly and concave inwardly. By the
opposition of the two concave aspects, a complete central
tube is formed. The maxillary palpi are wanting in Anosia,
and in most of the butterflies, although present in a one- or
two- or even several-segmented condition among most of
the moths.

Labium. — The labium is a fixed, semi-membranous sclerite,
triangular in outline, with its apex projecting cephalad and
joining the maxillar proboscis at its base. The labial palpi
are large, three-jointed, and covered with scales, and normally
project cephalo-dorsad. They are inserted on tumid spaces
on the base of the triangular labium, and the first joint is
pedicellate.

Make a drawing of the cephalic aspect of the head show-
ing the fixed and movable parts.

CHAPTER VII.
THE VENATION OF THE WINGS OF INSECTS.*

INTRODUCTION.

In form an insect's wing is a large, membranous append-
age, which is thickened along certain lines. These thick-
ened lines are termed the veins or nerves of the wing ; and
their arrangement is described as the venation or neuration of
the wings.

It has been found that the venation of the wings of closely
allied insects is very similar, and that great differences in
this respect exist between insects remotely connected. Hence,
the wings afford excellent characters for use in the classifica-
tion of insects. In fact, as slight differences in venation are
easily observed, the wings being spread out like an open
page, these differences are probably the most available char-
acteristics of winged insects for taxonomic work. It is im-
portant, therefore, that the student of entomology should
learn early in his course the more important facts regarding
this subject.

A careful study of the wings of many insects has shown
that the fundamental type of venation is the same in all of
the orders of winged insects. But this fact is evident only

'The material for this chapter has been drawn largely from an essay by the
writer, entitled Evolution and Taxonomy, published in The Wilder Quarter- Cen-
tury Book, Ithaca, 1893, and from a series of articles entitled The Wings of In-
sects, by J. H. Comstock and J. G. Needham, published in The American
Naturalist, vol. xxxii. (1898), and vol. xxxiii. (1899).

86

87

when the more primitive or generalized members of different
orders are compared with each other. In most of the orders
of insects the greater number of species have become so
modified or specialized as regards the structure of their wings
that it is difficult at first to trace out the primitive type.

NOTE. — The student should have a clear idea of the significance of the
terms generalized and specialized, which are now much used in biology.
Generalized indicates a primitive condition, a nearness to ancestral forms.
Thus, the most generalized member of a group (as a family or an order) is
that member which most clearly resembles the ancient progenitor of that
group. Specialized, on the other hand, indicates remoteness from the
primitive type, an adaptation to more special conditions of existence. Thus,
the most specialized member of a group is the one that departs most widely
from the ancient progenitor of that group.

These terms are used in a comparative sense ; thus, a highly specialized
form may be regarded as generalized when compared with forms that are
still more highly specialized.

The specimens indicated for the student to study in the
following part of this course have been selected with care to

Sc

FIG. 2. — Wing of Rhyphus.

illustrate gradually increasing degrees of divergence from
the primitive type. In the case of each order studied, the
work begins with a comparatively generalized form, and
passes step by step to those that are more specialized.

The flies of the genus Rhyphus afford good examples of
comparatively generalized wings. By studying a wing of
one of these flies and the accompanying figure (Fig. 2) the

88

student can gain a good idea of the type of the wings of in-
sects belonging to the order Diptera, and have a standard
with which to compare wings of insects of other orders.

Longitudinal veins and cross-veins. — The veins can
be grouped under two heads : first, longitudinal veins, those that
normally extend proximo -distad ; and second, cross-veins,
those that normally extend more or less nearly cephalo-
caudad. In Figure 2, three of the cross-veins are indicated
by arrows, near the middle of the wing ; two other cross-
veins are represented near the the base of the wing, but are
not lettered. All other veins represented in this figure are
longitudinal veins.

The insertion of the word normally in the above definitions
is important ; for it is only in comparatively generalized
wings that the direction of a vein can be depended upon for
determining to which of these two classes it belongs. A
little later the student will study wings in which the direc-
tion of some of the longitudinal veins has been so modified
in the course of specialization that they extend transversely
(i.e., cephalo-caudad), and some cross-veins extend in a longi-
tudinal direction (i.e., proximo-distad).

Simple veins and branched veins. — Veins are either
simple or branched. The veins lettered Sc and 1st A in
Figure 2 are simple veins ; between these there are three
branched veins.

In the case of branched veins the entire vein, including all
of its branches, is often referred to as a single vein. Thus
the third vein in the wing of Rhyphus, counting the thick-
ened, cephalic margin of the wing as the first vein, is termed
the radius or vein R ; and by this expression we include
both the main stem of the vein and its three divisions. On
the other hand, each division of a branched vein is often
termed a vein. Thus the first division of the radius, count-
ing from the cephalic margin of the wing, is termed radius-

89

one or vein R^ and the second division, radius-two or vein
Rv and so on till all are numbered.

NOTE. — In the most generalized flies known to us, the radius is five-
branched. But in most flies some of the branches of this vein coalesce so
that the number of apparent branches is less than five. In Rkyphits veins
A'j and A'3 coalesce so as to appear as a single vein. In order to indicate
that this apparently simple vein is composed of two veins, and in order thai
homologous veins in different insects shall bear the same designation, this
compound vein is termed radiiis-two-plus-three or vein A'~ + 3. In the same
way, what appears to be the third branch of the radius in Rhvphns is really
the fourth and fifth coalesced, and is, therefore, designated as radiits-four-
phts-five or vein A^ + 5. The tracing, out of the homologies of the branches
of veins is often very difficult ; but it is of the greatest importance in deter-
mining the relationships of different genera or of families.

Names of the longitudinal wing-veins. — There have
been many different sets of names applied to the veins of
wings. Not only have the students of each order of insects
had a peculiar nomenclature, but in many cases different
writers on the same order have used different sets of terms.
This condition of affairs was incident to the beginning of the
science, the period before the correspondence of the veins in
the different orders had been worked out. But now the time
has come when it is practicable to apply a uniform nomencla-
ture to the longitudinal wing-veins of all orders ; and the
following set of terms has been proposed for that purpose :

Costa. — The vein extending along the cephalic or costal
margin of the wing is the costa.

Subcosta. — Immediately caudad of the costa and extending
parallel with it, is a vein, which is usually simple in flies ; this
is the sub costa (Fig. 2, Sc\

Radius. — Immediately caudad of the subcosta there is a
vein which in generalized insects is always branched ; this is
the radius. In Rhyphus, the radius is three-branched (Fig. 2,

90

Media. — Traversing the middle of the wing there is a
longitudinal vein which is always branched in generalized
insects ; this is the media. In Rhyphus the media is three-
branched (Fig. 2, Mv J/2, and J/3).

Cubitns. — The third and last of the branched veins in flies
is the cubitus. This vein is two-branched in Rhyphus (Fig.
2, O/t and O/J.

Anal veins.— Caudad of the cubitus there is in Rhyphus a
single well-developed vein ; this is termed an anal vein. As
in more generalized insects there are three anal veins, and as
this is believed to be the first of the series, it is designated
the first anal vein (Fig. 2, \st A). A rudiment of the second
anal vein persists in Rhyphus j this is indicated in the figure
by a dotted line, at the left of the letter A.

Designation of the longitudinal wing-veins by numbers. — Several
writers have designated the longitudinal wing-veins by numbers. In Corn-
stock's Manual for the Study of Insects both the names given above and
numbers are used. The following table indicates the correspondence of the
names and numbers ; and Figure 3 represents the wing of a butterfly, with
the veins and cells numbered according to the system used in that manual.

Costa = vein I. Cubitus = vein VII.

Subcosta = vein II. 1st anal vein = vein VIII.*

Radius = vein III. 2d anal vein = vein IX.

Media = vein V. 3d anal vein = vein X.

It will be observed that in the above table the numbers IV and VI are
omitted. At the time the Manual for the Study of Insects was published, it
was believed that two other longitudinal veins (the so-called premedia and
postmedia) were present in certain orders of insects, and the numbers IV
and VI were applied to these veins. It has since been determined that this
conclusion was based on an error.

Certain writers number the wing veins without omitting the numbers IV
and VI, designating the media as vein IV and the cubitus as vein V.

* As the anal furrow, which is described later, was supposed to represent the
first anal vein, it is numbered VIII in the descriptions of wings of Diptera and
Hymenoptera in the work cited, and the true first anal vein is numbered IX.

There are still other writers who do not regard the costa as a true vein,
and, therefore, designate the subcosta as vein I.

The result is that there are three distinct systems of numbering the wing-
veins, in addition to several old systems which were applied to single orders.
It seems better, therefore, to designate the wing-veins by names, and use
abbreviations of these names in lettering figures.

Names of the cross-veins. — In the Diptera and in cer-
tain other orders of insects there are so few cross-veins that
it is practicable to apply names to them ; these are as follows :

The humeral cross-vein. — This is a single cross-vein ex-
tending from the subcosta to the costa near the base of the

C

FIG. 3. — Fore wing of a butterfly with the veins and cells numbered.

wing. This is the most constant of all of the cross-veins.
It is represented in Figure 2, but is not lettered.

The radial cross-vein. — This is a cross-vein which divides
cell R^. (The cells are denned a little later.) The radial
cross-vein is not represented in Figure 2.

The radio-medial cross-vein. — This is a cross-vein extending
from the radius to the media, usually near the center of the
wing, and is designated by the abbreviation ;•-/;/. When in
its typical position this cross-vein extends from vein J?t+s to
vein J/I+2 ; this results in one end being opposite cell R^ and
the other end opposite cell ist M .

92

The medio-cubital cross-vein. — This is a cross-vein extending
from the media to the cubitus, usually near the center of the
wing. It is designated by the abbreviation m-cu. When in
its typical position this cross-vein extends from a point near
the base of vein J/3f4 to a point near the base of vein Cur

The medial cross-rein. — This is a cross-vein extending
from vein J/a to vein Mz ; it is designated by the abbrevia-
tion in. The presence or absence of this cross-vein is often
a character of considerable taxonomic importance.

The arculus. — In many insects there is what appears to be
a cross-vein extending from the radius to the cubitus near
the base of the wing. This has been termed the arculus by

writers on the
Odonata, and the
use of this term

f* \. l+^-CV ~'~4

c*- ~ <- has been extended

FIG. 4. — The arculus, diagrammatic. ji Orf1ers jn

which there is a similar arrangement of the veins in this part
of the wing. The arculus is designated by the abbreviation
ar. Usually when the arculus is present the media appears
to arise from it. The fact is, the arculus is compound, being
composed of a section of the media and a cross-vein. The
structure of this part can be clearly seen in the Odonata
(Fig. 4). In Ryphus (Fig. 2) the arculus. appears as a simple
cross-vein extending from the radius to the cubitus, and a
part of the base of the media is atrophied.

Designation of the cells of the wing.— The thin spaces
of the wings which are bounded by the veins are called cells.
In descriptions of wings it is often desirable to refer to one
or more of the cells. It is necessary, therefore, to have a
nomenclature of the cells of the wing, as well as of the wing-
veins.

Having named the wing-veins, the simplest possible
method of designating the cells of the wing is to apply to

93

each the abbreviation of the name of the vein that forms its
cephalic (front) margin. It should be borne in mind, how-
ever, that by modifications of the typical arrangement of the
wing-veins, a vein that normally forms the cephalic margin
of a cell may apparently bear a very different relation to it ;
and this must be taken into account if we are to apply the
same term to homologous cells throughout the insect series.

The cells of the wing fall naturally into two groups : first,
those on the basal part of the wing ; and second, those
nearer the distal end of the wing. The former are bounded
by the principal veins ; the latter, by the branches of the
forked veins ; a corresponding distinction is made in desig-
nating the cells. Thus the cell lying behind the main stem
of the radius and on the basal part of the wing is designated
as cell R ; while the cell lying behind the radius-one is
designated as cell R^.

It should be remembered that the coalescence of two
veins results in the obliteration of the cell that was between
them. Thus when veins R^ and R^ coalesce, as in Rhypkus
(Fig. 2), the cell lying behind R^^ is cell R^ and not cell
7?2+3, cell R^ having been obliterated.

When one of these principal cells is divided into two or
more parts by one or more cross-veins, the parts may be
numbered, beginning with the proximal one. Thus in Rhy-
phus (Fig 2) cell M^ is divided by the medial cross-vein into
two parts, which are designated as cell ist M^ and cell 2d M^
respectively.

The application of this system of naming the cells of the
wing is an easy matter in those orders where the wings have
few veins ; but in those orders where many secondary veins
are developed it is more difficult of application. In the lat-
ter case we have to do with areas of the wing rather than
with separate cells. Thus, for example, it will be seen later
that in certain Neuroptera the area R is divided by several

94

longitudinal veins, which are connected by many cross-veins,
the area R^ (which is strictly homologous with cell ^?2) being
composed of a large number of secondary cells.

The furrows of the wing. — The wings of comparatively
few insects present a flat surface ; in most cases we find that
the membrane is thrown into a series of folds or corruga-
tions. This corrugating of the wing in some cases adds
greatly to its strength. This is well shown by the wings of
dragon flies ; and in most orders the costal margin of the
wing is strengthened by a fold between the costa and the
radius, the subcostal fold. In other cases, the corrugations
are the result of a folding of the wing when not in use ; this
is well shown in the anal area when this part is broadly ex-
panded.

It rarely happens that there is occasion to refer to indi-
vidual members of either of these classes of folds, except,
perhaps, to the one that has just been designated as the sub-
costal fold. But there are three other furrows which it is
necessary to designate, as they are frequently referred to.
These are the anal furrow, the median furrow, and the
nodal furrow. Only the first of these is well-marked in
the Diptera ; but for sake of completeness all are defined
here.

The anal furrow. — This is a longitudinal furrow which is
usually between the cubitus and the first anal vein. In the
figure of the wing of Rhyphus (Fig. 2), it is represented by
a dotted line immediately behind the cubitus. In the order
Diptera it is always in this position if present.

The median furrow. — This is a longitudinal furrow which
is usually between the radius and the media. It is well
marked in many of the Hemiptera, where it separates the
embolium from the remainder of the corium ; and in the
Hymenoptera its course is marked by a series of weak spots
(bullae) in certain veins.

95

The nodal furrow. — This is a transverse suture beginning
at a point in the costal margin of the wing, corresponding
to the nodus of the Odonata, and extending towards the
inner margin of the wing. It crosses a varying number of
veins in different orders of insects.

The furrows of the wing are in no sense homologous or even analogous
to veins. More than this, the relative positions of the furrows and of the
wing-veins are not constant ; for it frequently happens that the course of a
vein has been so modified that it crosses the line of a furrow and the rel-
ative positions of the two are thus reversed. If this fact had been under-
stood by Adolph we would have been spared his misleading theory of alter-
nating concave and convex veins.*

Margins of wings. — An insect's wing is more or less
triangular in outline ; it, therefore, presents three margins ;
the costal margin (Fig. 3, a-b) ; the outer margin (Fig. 3, b-c),
and the inner margin (Fig. 3, c-d).

Angles of wings. — The angle at the base of the costal
margin (Fig. 3, a) is the humeral angle ; that between the cos-
tal margin and the outer margin (Fig. 3, b) is the apex of
the wing ; and the angle between the outer margin and the
inner margin (Fig. 3, c) is the anal angle.

The typical branching of the wing-veins.— In order
to determine the homologies of the branches of a forked
vein when some of the cells have been obliterated by the
coalescence of branches, it is necessary to know what was
the primitive type of branching of this vein. For this rea-
son an effort has been made to determine the probable
structure of the wing of the primitive winged insect,

In the study of the development of wings, it has been
found that in the more generalized insects the cavities of
the longitudinal wing-veins are formed about tracheae, and

* G. Ernst Adolph, Ueber Insectenflugel. .\'ova Acta der ksl. Leop.-Carol-
Deutschen Akademie der Naturforscher, Bd. xli, pp. 215-251. 1879.

96

that these tracheae exhibit a striking similarity in their origin
and mode of branching in the nymphs and pupse of the
more generalized members of most of the orders of insects.
We have been able, therefore, to present a hypothetical type,
which we believe represents approximately what was the
arrangement of the tracheae in the nymph of the primitive
winged insect (Fig. 5), and, as the wing-veins of the adult
are developed about the tracheae of the wing of the nymph,

FIG. 5. — Diagram representing the hypothetical arrangement of the tracheae in
a wing of a nymph of the primitive winged insect.

the same figure will serve to indicate the probable mode of
branching of the wing-veins in the adult of the primitive
winged insect.

The radial sector. — When the radius preserves its prim-
itive mode of branching, it separates at its first fork into
two unequal parts ; the first of these is vein R, ; the other
gives rise to the remaining four branches of the radius (Fig.
5). This second part of the radius, including its branches,
is termed the radial sector or vein Rs,

97

IDENTIFICATION OF THE WING-VEINS AND OF THE CELLS OF
THE WING IN DIPTERA.

As the chief object of the following work is to give the
student training in tracing the homologies of wing-veins,
comparatively little information will be given directly. The
student will be furnished in each case with the wing to be
studied, and his studies should take the following course :—

Directions for the study of wings. — Make a drawing
of the wing, based upon a careful study of it with a com-
pound microscope, using a low power. The drawing should
be first made with a pencil ; after it has been criticised by
the teacher, the lines should be inked ; ink the lines repre-
senting the media with red ink, use black ink for the re-
mainder of the wing, including the medial cross vein. Make
the drawing on a sufficiently large scale so that each vein
can be represented distinctly ; in most cases the drawings
should be somewhat larger than Figure 3.

Number each vein and cell of the wing.

Note the more important features of its venation, and
especially the more important departures from the primitive
type of the order as indicated by the generalized form first
studied. In the Diptera the wing of Rhyphus (Fig. 2) may
be used as a generalized type, although in certain respects
other wings will be found to be more generalized.

The following are some of the more important points to be
noted : Whether the subcosta is simple or forked at the tip ;
the number of the branches of the radius ; in this connection
determine which of the radial cells has been obliterated by
the coalescence of branches of the radius (study Fig. 5) ; the
position of the radio-medial cross-vein; the number^ of the
branches of the media (in none of the common Diptera has
the media more than three branches ; and the mode of dis-
appearance of vein M \ in this order has not been determined

98

as yet. For this reason the student need not take this vein
into consideration in his studies of dipterous wings) ; the
division or not of cell J/2 ; the presence or absence of cell
J/3 ; the courses of the branches of the cubitus ; the extent
of the anal furrow ; and the course of the anal vein.

Wing of a Tabanid. — A specimen of one of the horse-
flies, Tabanns, will be given the student for examination.
Observe the subcostal fold, and note that this corrugation stiff-
ens the wing.

Make a drawing of a mounted Tabanid wing, which will
be furnished on application to the instructor. Note that in
the mounted wing the subcosta is more or less concealed by
the radius, although the two veins are distinct, as was seen
in the unmounted specimen. Represent these two veins as
slightly separated in your drawing.

In the description of this wing, state in what respect it is
more generalized than that of Rhyphus, and in what respect
it is more specialized.

Wing of an Asilid. — A wing of a robber-fly of the genus
Erax will be used as an example. Note a method of coa-
lescence of veins not exhibited by RhypJnis.

Wing of a Bombyliid. — The example used is a wing of
Pantarbes, one of the bee-flies.

Wing of a Scenopinid. — The wing used is that of a com-
mon window-fly, Sccnopinus-.

Wing of an Empidid. — The wing used is that of Rham-
phomyia, one of the dance- flies.

Wing of a Muscid. — The wing used is that of the com-
mon house-fly, Musca doinestica.

Wings of Dilichopodids. — The wings of two of the
long-legged flies will be used. The first belongs to the genus
Psilopns ; the second to the genus Dolichopus.

Wing of a Syrphid. — The wings of a fly of the genus
Syrphus will be used. Note the vein-like structure be-

99

tween the radius and the media ; this is termed the spurious
vein.

Wing of Culex. — The wing of a mosquito is used as an
example of the venation of the midge-like flies. In these
the number of the branches of the radial sector is reduced in
away different from that seen in the families previously stud-
ied. Compare with the Asilid, the Bombyliid, and the Sceno-
pinid.

THE WINGS OF LEPIDOPTERA.

As the wings of Lepidoptera are covered with scales, it is
difficult to determine the nature of their venation without
specially preparing them for this purpose. After a student
has become familiar with the type of venation characteristic
of the order, he can usually determine the course of any
particular vein by putting a drop of chloroform on the part
of the wing to be examined ; this will render the veins more
distinct for a few seconds. Or the scales can be removed
from a small part of the wing with a small artist's sable
brush. But when a very careful study of the venation of a
wing is to be made, it should be bleached and mounted on a
card or on a glass slip, in order that it may be studied with
a compound microscope. The following is the method of
bleaching wings : —

1. Remove the wings carefully so as not to break the fren-
ulum if there be one ;* it is well to remove the patagium
first. f

2. Dip the wings in alcohol in order to wet them.

3. Immerse them for an instant in hydrochloric acid (muri-
atic acid). Use for this purpose dilute acid, one part acid to
nine parts water.

* The frenulum is a strong spine or bunch of bristles borne by the hind wing
at the humeral angle in most moths.

t The patagia are scale-like appendages at the bases of the fore wings.

100

4. Put them in Labaraque solution with the upper surface
of the wings down, and leave them there till the color has
been removed from the scales. If a wing bleaches slowly,
the process can be hastened by dipping it in the dilute acid
and returning it to the Labaraque solution from time to time.
This solution can be procured of most druggists. It deteri-
orates if left exposed in strong sunlight. If it cannot be ob-
tained use an aqueous solution of chloride of lime.

5. When a wing is bleached, put it in alcohol and leave it
there till after it floats. This is to wash off the Labaraque
solution. The wing can then be mounted on a card. But it
is better to mount it as described below.

6. Transfer the wing to a clearing mixture, if it is to be
mounted in balsam, and leave it there five or ten minutes.
This is to remove any water there may be on it. A good
clearing mixture can be made by mixing two parts by measure
of carbolic acid crystals and three parts of rectified oil of
turpentine-

7. Put the wing on a glass slip with considerable clearing
mixture under it to avoid bubbles ; put Canada balsam on
top, and cover with a cover glass. In the case of small wings,
it is best to transfer them from one solution to another, and
to the glass slip by means of a camel 's-hair brush.*

Wings bleached and mounted in this way make an im-
portant addition to a collection. The slides should be care-
fully labelled ; and the insect from which the wings were
taken should be kept with the slide. It is our practice to re-
move always the wings from the right side, and then to mount
the slide in the collection at the right of the insect from
which the wings were taken. Uniformity in this respect adds
greatly to the appearance of the collection.

* In the case of very small wings, as those of Tineids, the very fine veins are
more distinct when mounted in glycerine-jelly than when mounted in Canada
balsam.

101

Wings of Hepialus Mounted specimens of the two

wings of one side of a moth belonging to the genus Hepialus
will be furnished the student for study. Be very careful of
th^ specimens, as moths of this genus are rare in this
country.

The membranous lobe near the base of the inner margin
of the fore wing is \hejugum. This extends under the costal
margin of the hind wing, while the greater part of the inner
margin of the fore wing overlaps the hind wing. This ar-
rangement assures the acting together of the two wings.

Wings of a Cossid. — Mounted wings of one of the
Cossidce will be furnished the student for study.

Wings of the monarch butterfly. — The student will
be furnished with specimens of the two wings of one side of
the monarch butterfly, Anosia plexippus.

Study the fore wing first. Explain the significance of the
three short spurs that project into the distal end of the large
cell near the middle of the wing.

Wings of frenate moths. — Specimens of moths be-
longing to the family Noctitidce. will be used as illustrations of
Lepidoptera in which the frenulum is well developed. Two
specimens, a male and a female of the same species, should be
studied if practicable.

Remove the wings of the right side of the female, and
bleach and mount them.

Figure these wings.

Remove the wings of the right side of the male, and bleach
and mount them.

Figure these wings.

Describe the secondary sexual distinction exhibited by the
wings of this species.

How could one of these types have been derived from the
other ?

Study the wings of the male that have not been bleached,

IO2

and note the fremdum hook on the fore wing, which receives
the tip of the frenulum. It may be necessary to remove
some of the hairs from the base of the wing. Use a small
sable brush for this.

Study the unbleached wings of the female, and note the
absence of a frenulum hook.

Compare the hind wing of the monarch butterfly with the
hind wings of these moths, and discuss the differences be-
tween them.

THE WINGS OF HYMENOPTERA.

The determination of the homologies of the wing-veins of
Hymenoptera is very difficult ; as even in the most general-

FIG. 6. — The veins of a typical hymenopterous wing.

ized of the living members of the order, the venation of the
wings departs widely from the primitive type. For this
reason no student should begin his study of the venation of
wings with hymenopterous insects. In the following dis-
cussion it will be assumed that the student has carefully per-
formed the work on the wings of Diptera outlined in the
preceding pages ; and the first step for him to take at this
point in his studies is to take his drawings of dipterous
wings and review that work.

103

The method of specialization of wing-veins which has
taken place in the Hymenoptera can be most easily seen by
a study of the fore wings of certain sawflies. The most use-
ful for this purpose that we have found belong to the genera
Pamphilius and Macroxyela. If we are right in our interpre-
tation of the wings of these insects, there is preserved in
each genus all of the primitive wing-veins with a single ex-
ception. And, as in each of these genera a different vein is
lost, we are able to make a figure of a typical wing from a

Sf

FIG. 7.— The cells of a typical hymenopterous wing."

study of the two genera. Figures 6 and 7 represent such a
wing ; in the former the veins are lettered ; in the latter, the
cells. f

In the wings of these sawflies the anal furrow and the
median furrow are both well marked, and are in the typical
positions ; that is, the anal furrow is immediately in front of
the first anal vein, and the median furrow is in front of the

* The cell lettered S is probably &-2. When it is thickened and opaque, as
is frequently the case in this order, it is termed the stigma.

t Figures 6 and 7 represent the venation of the fore wing of Pamphilius, except
that vein /?,,, which is lacking in this genus, is added. This vein is well pre-
served in Macroxyela, but in Macroxyela vein Cu.t is lost. See Comstock.
Manual for the Study of Insects, p. 606, tor figures of the wings of these two
genera.

104

media. The furrows are represented by dotted lines in the
figures.

In the anal area (i.e., that portion of the wing back of the
anal furrow) the three typical veins are preserved ; but they
coalesce to a considerable extent, both at the base and near
the margin of the wing.

In the basal part of the pre-anal area (i.e., that portion of
the wing in front of the anal furrow) the stems of the princi-
pal veins are as follows : the costa coincides with the costal
margin of the wing (Fig. 6, C) ; the subcosta (Sc) is well pre-
served and is forked ; back of the subcosta is a strong stem
formed by the coalescence of the other three veins ; the
cubitus (Cii) soon separates from the stem, extending in a
curve towards the anal furrow ; while the radius and the
media coalesce for about half their length. In order to
make these veins more distinct in the figure we have marked
the free portion of the media with cross lines.

When we pass from the consideration of the main stems to
a study of the branches, we meet a much more complicated
problem, a problem which could not have been solved by a
study of Hymenoptera alone. But a knowledge of the meth-
ods of specialization of the wings of Diptera gives a key to an
understanding of the wings of Hymenoptera.

We will study first the branches of the cubitus. Spread
out before you your drawings of the wings of the following
insects, and arrange them in the order named : a Bombyliid,
a Scenopinid, and an Empidid. Now study the figure of a
wing of Rhyphus (Fig. 2, p. 87) and note that while in Rhyphus
veins Cit^ and 1st A retain their primitive position, in the
three wings named above these two veins exhibit varying de-
grees of coalescence.

A similar method of specialization has taken place in the
Hymenoptera, but in this order both branches of the cubitus
coalesce with the first anal vein ; and this coalescence has

proceeded so far that both branches cross the anal furrow
and end in the anal vein remote from the margin of the wing.
(See Fig. 6.)

It should be noted that vein O/2 is rarely preserved in this
order, even in the more generalized forms. We have found
it only in the genus Pamphilius. In Macroxyela* the posi-
tion of the fork of the cubitus is indicated by a bend in this
vein.

If the branches of the media be now examined, it will be
seen that vein J/t (Fig. 6) extends longitudinally near the
centre of the distal part of the wing, its primitive course
being modified slightly if at all. Vein Aft follows a course
similar to the course of this vein in the Bombyliid ; so also
does the medial cross-vein (Fig. 6, m). A comparison of
the position of cells J/,, ist M^ and 2d J/2 in the Bombyliid
and in the typical hymenopterous wing (Fig. 7) is very in-
structive.

Returning to Pamphilius (Fig. 6), we see that vein M3
coalesces with the first anal vein, crossing the anal furrow
near the margin of the wing. It is evident that the forces
that are causing the branches of the cubitus to migrate along
the first anal vein and towards the base of the wing are ex-
erting a similar influence on this vein. It is also evident
that vein Mt and Cu^ coalesce at the tip, and that the migra-
tion of the united tips of these veins (marked On in the figure)
towards the base of the wing has so modified the course of
that part of vein J/4 which is still free that this part of this
vein extends towards the base of the wing. This change is
very similar to the change in the course of vein O/a in the
Empidid.

A curious result of this change in the direction of the
course of vein J/4 is that the cell J/4 has been closed and

* Comsttfck, loc. ctt., Fig. 735.

io6

pressed back to the centre of the wing (Fig. 7, M4), and now
lies in front of the free portion of the vein J/4 instead of be-
hind it.*

Let us now consider the courses of the branches of the
radius. Here again we can gain help from a study of dip-
terous wings. Observe in the Bombyliid (Pantarbes) the
coalescence of the tips of veins 7?5 and M^. In the Hymen-
optera a similar coalescence of veins R^ and M^ has occurred ;
but it has proceeded much farther, so that the free portion
of vein R^ in Pamphilius (Fig. 6, R^ is remote from the end.
of the wing and has the appearance of a cross-vein.

In the Hymenoptera vein R,^ has been followed in its
migration along vein M1 by vein J?4, which has now reached
a stage in Pamphilius that is quite similar to that reached by
vein R^ in Pantarbes. But like vein Rb it has the appearance
of a cross-vein.

From this it will be seen that the vein marked Mt in Fig-
ure 6 is really compound, as it includes the tips of veins
R^ and Jtt.

In PainpJiilius vein Rl is curved away from the costal
margin of the wing to make room for a stigma (Fig. 7, S),
and vein R^ ends in the costal margin a short distance before
the apex of the wing (Fig. 6). Vein R^ has been lost in this
genus, but is well preserved in certain closely allied forms.f
and is, therefore, represented in the figure.

While the tips of the branches of the radial sector have
migrated away from the apex of the wing, the bases of
these branches coalesce in the opposite direction ; from these

* At the time that the figures in Comstock's ^lanual were prepared it was
believed that the media was typically three-branched. For that reason the vein
which we now regard as vein /l/4 was believed to be a cross-vein. The inter-
pretation given above accords better with what we have since learned to be the
typical form of the media.

t See page 103, footnote.

107

two causes results the transverse bracing of the radial area
of the wing, which is a very characteristic feature of the
venation of the wings in this order.

The details of these changes will be made clear by an ex-
amination of Figures 8 and 9. The former represents the
primitive mode of branching of the radius ; the latter, the
radial area of the typical hymenopterous wing (Fig. 6). In
the hymenopterous type veins Jtz+3 and -/?4+s of the primitive

FIG. 8.— The typical radius.

FIG. 9. — The radius in Hymenoptera.

type coalesce so far that the branches of the sector arise
from a common stem ; and the tips of all of them have
moved away from the apex of the wing, veins ^?2and R^
following the costal margin of the wing ; and veins R^ and
R^ following vein Mr

In the Hymenoptera the radial cross-vein is frequently
preserved; it is marked c v in figures 6 and 9.

The student who has followed this discussion and has
understood it will be prepared to make original investiga-
tions of the venation of the wings of Hymenoptera. But no

loS

student should take up the work indicated below before
everything in this discussion is clear to him.

Study the fore wings of the insects named below. It is
not best to attempt to determine the homologies of the veins
of the hind wings at first, owing to the great reduction of
wing-veins that has taken place in these wings. The direc-
tions for the study of wings given on page 97 will apply here
except that Figures 6 and 7 instead of Figure 2 will be used
for comparison. Indicate the media with red ink.

The fore wings of Tenthredinids. — The wings of two
saw flies will be used as examples of different degrees of
specialization :

(a.) Macroxyela.

(b.) Pteronus. The currant sawfly.

The fore wing of a Siricid. — The best genus of the
Siricidae for this study is Sirex. The more common, Tremex,
is more difficult.

The fore wing of a Sphecid.— Use for this purpose a
wing of the common mud-dauber, Pdopceus.

The fore wing of an Ichneumon-fly.— A species of
Ichneumon will furnish an example.

The fore wing of a Braconid. — Compare with the wing
of an Ichneumon-fly. Color vein J/3 red and the medial
cross vein black.

The fore wing of the Honey-bee.

THE WINGS OF NEUROPTERA.

The foregoing studies of the wings of Diptera, Lepidop-
tera, and Hymenoptera have shown that in none of the
genera studied has the number of the branches of any vein
exceeded that of our hypothetical type (Fig. 5), and that in
none of them have all of the branches of all of the veins re-

109

mained distinct. These wings illustrate, therefore, what has
been termed specialization by reduction.

There are, however, several orders of insects in which, as
a rule, some of the wing-veins have a greater number of
branches than in the hypothetical type. These illustrate
what has been termed specialization by addition.

Among the orders in which specialization of wing-veins
by addition has taken place is the Neuroptera ; and several
genera of this order will be studied as examples of this
method of specialization. We will, however, first point out
the more important features of specialization of wing-veins
by addition.

In speaking of an increase in the number of veins, refer-
ence is made only to a multiplication of the branches of the
principal veins. In no case is there an increase in the num-
ber of principal veins. And this increase in the number of
branches may be confined to one or two of the principal
veins in the preanal area, while the number of the branches
of some of the other veins may be reduced, the expanding
of some parts of the preanal area resulting in a crowding of
other parts. In some cases we will find that the multiplica-
tion of wing-veins extends to the anal area also ; in others
we will find the anal area greatly reduced. But even in
those cases where the anal area is reduced, the total result
has been the production of a r^any-veined wing.

In the many-veined wings both the longitudinal veins and
the cross-veins are increased in number. In most cases
where there are many cross-veins it is impracticable to dis-
tinguish from others those particular cross-veins to which we
applied special names in describing the few-veined wings.
(See page 91.) But in the case of the longitudinal veins it
is necessary to distinguish the primitive veins, that is, those
of our hypothetical type, from the veins that have been de-
veloped in addition to these. For if this is not done it will

IIO

be impossible to point out the changes that have taken
place in the course of the development of each of the vari-
ous types of many-veined wings. We therefore apply the
term accessory veins to these secondarily developed longitu-
dinal veins, and retain the same nomenclature for the primi-
tive veins that we used in describing the few-veined wings.

The development of accessory veins. — Accessory
veins may be borne by any of the primitive longitudinal
veins ; and they may arise from either of the two sides of
such a vein. In most cases it is unnecessary to designate
the individual accessory veins, as, usually, it will be sufficient
for descriptive purposes to indicate the number of these
veins that have been developed upon a particular longitudi-
nal vein. In fact, in certain cases more than this could not
well be done, owing to the irregularity of the veins. On the
other hand, in many cases the accessory veins borne by a
single primitive vein present a high degree of regularity,
and it is evident that they have been developed in a regular
sequence. Under these circumstances it is practicable to
designate them individually ; and we have devised the fol-
lowing method for this purpose.

The accessory veins arising from one side of a single
primitive vein are considered as a single set, and to each set
of veins a distinct set of numbers is applied, beginning with
the oldest (i.e., the first-developed) member of the set.

By this method homologous veins, when a homology ex-
ists, will bear the same number. But it should be remem-
bered that as accessory veins have arisen independently in
many different groups of insects, it often happens that acces-
sory veins similar in position, and bearing the same number
in our system, are merely analogous and not homologous.

In order to apply this system it is necessary to know, in
the case of each group of insects studied, the sequence in
which the members of the particular set of veins under con-

Ill

sideration have been developed. For additions to such a set
of veins may be made to the distal end of the series, or to
the proximal end, or may be interpolated at some distance
from either end.

We will illustrate these principles by a figure of the wing
of a nymph of a cockroach (Fig. 10). We do not use for this
purpose a figure of a wing of a 'neuropterous insect, as that
would lessen the value, as a means of training, of the study
of neuropterous wings which the student is to make. A

FIG. 10. — Hind wing of a nymph of a cockroach.

nymph is used here, because in the many-veined insects the
longitudinal veins, both primitive and accessory, are devel-
oped about tracheae ; and it is much easier to determine the
homologies of the tracheae of an immature wing than it is to
determine the homologies of the wing-veins of the adult.
And, too, in this way we are able to eliminate the cross-
veins which are not preceded by tracheae in the cockroaches.
Accessory veins added distally. — If the radial trachea of tne
nymph of a cockroach be examined (Fig. 10, R\ it will be
seen that it bears many branches on its cephalic side ; each
of these branches is enclosed by a vein in the adult state.
The number of these veins is much gre'ater than that of the

112

hypothetical type. A comparison of the wings of different
species of cockroaches shows that the increase in the num-
ber of the branches of the radius has been greater in some
than in others ; and a study of the one figured indicates the
method of increase, which is doubtless as follows : the
branches have been added, one after another, to the tip of
the trachea, R, there being a migration of the base of each
accessory trachea towards the base of the wing, thus making
room for the addition of new branches. In this case the
first accessory vein is the proximal one ; but in this particu-
lar instance it is impracticable to number the accessory
veins, owing to a splitting of some of them which is taking
place.

Accessory veins added proximally. — A study of the cubital
trachea of the nymph of the cockroach figured above (Fig.
10, Cii] shows that accessory veins are being developed on
the caudal side of vein Cuv It can also be seen that the
distal members of the series of accessory trachete are well-
developed, and that the growth of additional ones is taking
place in the disk of the wing at the proximal end of the
series. In this case the first accessory vein is the distal one,
and the accessory veins should be numbered as indicated in
the figure.

Accessory veins interpolated. — Reference has been made above
to a splitting of some of the accessory trachene developed on
the cephalic side^f the radial trachea in the cockroach under
consideration (Fig. 10). As a vein is developed about each
of the divisions of these tracheae, it is evident that at the
same time that accessory veins are being added distally to
this series others are being interpolated. In cases of this
kind it is impracticable to number the members of a series of
accessory veins.

The suppression of the dichotomous branching of
veins. — In the more highly specialized of the many-veined

insect wings there exists a type of branching which is very
different from that of our hypothetical primitive type. An
examination of Figure 5, which represents the latter, will show
that in every case
the forked veins are
branched dichoto-
mously, while in the
many-veined wings
the more character-
istic type of branch-
ing results in the
formation of pecti-
nate veins; this
pectinate type of
branching is well
shown by the cubi-
tus in a cockroach
(Fig. ro Cu).

The changes that
take place in the
development of the
pectinate type of
venation from the
dichotomous type
are of two kinds :
first, the develop-
ment of accessory
veins ; second, the
modification of the
primitive veins so
that they are no

longer dichotomously branched. The former has been dis-
cussed above.; we will now briefly refer to the latter. For
this purpose we will give a series of diagrams illustrating

FIG. ii. — Diagrams of several types of radius.

U4

severed types of branching of the radial sector. Each of
these figures represents a condition which exists in some
insect.

Figure na represents the typical or dichotomously
branched radial sector. Figure n/> represents a typical ra-
dial sector with the addition of some accessory veins on the
caudal side of vein Rr In this case the radial sector is
nearly pectinate, but not quite so, owing to the forked con-
dition of vein /t>4+5. In the form represented by Figure nc
veins Rt and Rb coalesce to the margin of the wing ; and in
this way the pectinate type is attained. In another insect
(Fig. IK?) the pectinate type has been attained by fission in-
stead of coalescence. Here veins R^ and Rb have split apart
till vein R arises from the main stem of radius.

p

When many cross-veins are present, the dichotomy of the
branching of the sector may be suppressed in still another
way, by the transference of the base of vein Rt to vein
R2+y All stages of this switching of the base of vein R4
occur in the ant-lions ; and two of them are represented by
Figures ne and n/.

In the genus represented by Figure ne the base of vein
Rt appears to be forked ; one arm of the fork arising from
vein R^ the other from vein Rz+y The former is the true
base of vein Rt ; the latter is a cross-vein which is assuming
the function of a base of this vein. In the genus repre-
sented by Figure u/ the switching has been completed,
vein Rt arising from vein R2+z.

In the foregoing illustrations comparisons of allied insects
have been made in order to determine the ways in which
the wings are being modified ; frequently a comparative
study of the fore and hind wings of a single insect is equally
suggestive, for it often happens that the two pairs of wings
exhibit different degrees of the same kind of modification,
and thus the course of the change is indicated.

A study of the causes of the changes which we are de-
scribing is beyond our present purpose, which is merely to
determine the homologies of the wing-veins. But we can
gain a hint of the probable reason for the development of
the pectinate type of veins without entering very deeply into
questions of the mechanics of flight.

It is obvious that many styles of flight exist among in-
sects, and that for the different styles of flight different
kinds of wings are required. In CoryJa/is, which will be
studied a little later, it can be seen that the wing is stiffened,
along a line parallel with the costal margin of the wing, by
the subcosta, the main stem of the radius, and veins R^ and
J\^. Back of this line there is a broad, flexible area, which
bends up daring the downward stroke of the wing, forming
an inclined plane, the pressure of which against the air
forces the insect ahead. The flexibility of this area of the
wing is increased by those changes which result in the for-
mation of the pectinate type of branching.

The wings of Sialis. — Among our more common neu-
ropterous insects those of the genus Sialis have retained the
most generalized condition of wing-venation. It is sug-
gested, therefore, that the student begin his practice in de-
termining the homologies of the wing-veins of Neuroptera
with a member of this genus. Make a drawing of the wings
and letter the principal veins, and the accessory veins.

The wings of Chauliodes.-

The wings of Corydalis. — In this genus the radial sec-
tor is an example of a high development of the pectinate
type of venation.

The wings of Ant-lions. — Photographs of the wings of
representatives of several genera of the Myrmeleonidae will
be furnished the student for study. The photographs repre-
sent the wings gre?*!y enlarged and are, therefore, much
more available for study than the actual wings. Each

photograph is labeled with the name of the genus it repre-
sents.

Spread out the photographs before you and study the
costal area of the wings • the costal area is the area between
the costa and the subcosta ; it corresponds to cell C of the
few-veined insects. Observe the varying degrees of com-
plexity of the cross-veins ; observe also the stiffening of the
area opposite the point where veins Sc and R coalesce, and
compare it with the stigma in the Hymenoptera.

Study the radial area of all of the wings, determine the
homologies of the branches of the radius in eooh, letter
them, and number the accessory veins. Also indicate with
pencil marks the way in which the suppression of the dichot-
omous branching has been brought about.

That part of the wing of these insects lying caudad of the
radius presents difficulties that could hardly be solved by a
study of adults alone. A study of the development of the
wings of an ant-lion has shown that the second of the two
principal branches of the media and vein C//t coalesce.
Study the fore wings, which are less modified than the hind
wings, and observe that the media appears to be a simple
vein for the greater part of its length, and that the cubitus
exhibits a well-marked fork before the middle of the wing.
This fork is the point of separation of veins Cu^ and Cur
Observe that near this forking of the cubitus there is what
appears to be an oblique cross-vein extending from the media
to the cubitus ; this is not a cross-vein, but is the beginning
of vein J/3+4, which coalesces with vein Cul for the greater
part of its length. Letter the branches of the media and o;
the cubitus on each photograph. After this work has been
criticised, trace the course of media with red ink and tne
courses of radius and cubitus with black ink, omitting tne
accessory veins.

ii;

THE TRACHEATION OF THE WINGS OF NYMPHS AND OF

PUP/E.

It has been found that, in the course of the development
of the wings of the more generalized insects, the tracheae
which traverse the principal veins are developed before the
veins appear, and that later the veins are developed about
these tracheae. It is evident, therefore, that much light
can be thrown upon questions regarding the homologies of
wing-veins by studies of the tracheae which precede them ;
and the following suggestions are given to aid students who
wish to make such studies.

If a living pupa or nymph be placed in formol (4$) the
tissues of the wings will be rendered translucent in a short
time. In the case of very delicate insects only a few hours
are required for this, but with larger ones with more opaque
wings it is necessary to leave them in the formol for several
days, or even for several weeks. While the formol renders
the tissues translucent, it does not soon penetrate the
tracheae, which are, therefore, left filled with air, and appear
as dark lines when the wing is examined with transmitted
light. Just after molting some wings are translucent, but
there are few so clear that a short stay in formol will not
make them clearer.

In order to study wings prepared in this way, they are
removed from the body and mounted in glycerine-jelly, care
being taken to cool the mount quickly so that the jelly will
not penetrate the tracheae In this way most beautiful
objects can be prepared, which will show the minutest rami-
fications of the tracheae.

Not only can the tracheae that precede the wing veins be
studied in this manner, but, if the wings be taken at the
right stage, the forming veins will appear as pale bands
when viewed by transmitted light. This is due to the fact

that at this time the veins are merely cavities, filled with
lymph, and are more translucent than the spaces between
them, which are occupied by tissue.

Unfortunately, however, this distinction is only temporary
in most specimens. As a rule, the entire wing becomes
transparent in a few hours after it is mounted in the glyce-
rine-jelly. ]t is necessary, therefore, to make drawings or
photo-micrographs promptly, in order to keep a record of
the courses of the veins.

On the other hand, the tracheae, as a rule, stand out more
sharply twenty-four hours after mounting, because of the
clearing effect of the glycerine-jelly upon the tissue of the
wing. But the making of drawings or photo-micrographs
of the tracheae should not be delayed long ; for the tracheae
soon become filled with the jelly, and are then practically
invisible.

The preparation of specimens. — Collect living nymphs
or pupae, place them in formol (4$), and leave them for a
time, as indicated above. The formol will make the wings
of the insects more translucent ; but it will not remove dark
colors from chitin. It is well, therefore, to select, at first,
the paler species for study.

^ When ready to mount a wing, spread a drop of melted
glycerine-jelly on a slide and allow it to cool.

Dissect off the wing to be studied, taking with it just
enough of the thorax to include the basal attachments of the
tracheae. The dissection may be made under water ; but the
wing should be removed from the water promptly, so that the
tracheae may not become filled with water.

Place the wing upon the solidified glycerine-jelly on the
slide ; and lower upon it a heated cover-glass, which will
cause the jelly to melt enough to envelop the wing.

Cool the mount quickly on ice, a marble slab, or some other
cold object. Rapid cooling is imperative, for in melted glyc-

H9

erine-jelly the tracheae soon become filled, and the smaller
ones are then invisible.

It is imperative, also, that the wings be handled with care.
Being sac-like structures, the tracheae are almost free within
them, and a slight pinch with forceps in the middle of the
wing may throw all of its tracheae out of place. It is better
to lift the wing by its thoracic attachments or upon a section
lifter.

Not every nymphal wing is fitted for this study. Just before
molting, and especially just before the last molting, the wing
becomes so crumpled within its old sheath that the course of
its tracheae can be followed only with difficulty.

The method of study. — So far as is practicable, the
studies of the tracheation of the wings of nymphs and of
pupae will be original investigations. For this reason, no
particular species is suggested for study. The student will
select the most available material, and will endeavor to make
an addition to our knowledge of this subject. The series of
articles in the American Naturalist, already referred to (see
page 86, note), may be used as a work of reference. A few
suggestions, drawn from the studies upon which those arti-
cles were based, are given here : —

Among the more available subjects for the beginner in
this line of work, are the pupae of moths and the nymphs of
Orthoptera. The former illustrate specialization by reduc-
tion ; the latter specialization by addition. During the win-
ter, when it is difficult to collect Orthoptera, the nymphs of
stone-flies (Plecoptera) may be used instead. These can be
found under stones in the beds of streams.

In many insects the costal trachea is wanting or is but
slightly developed. It does not follow, therefore, that the
trachea nearest the costal margin of the wing is the costal
trachea. In most cases, the radial trachea can be identi-
fied easily, and it will serve as a starting point for the

120

determination of the homologies of the other principal
tracheae.

In most orders of insects the longitudinal veins can be
distinguished from the cross-veins by the fact that the cross-
veins are not preceded by tracheae.

In some of the many-veined insects, as Odonata, the
cross-veins, as well as the longitudinal veins, are preceded
by tracheae ; there being, in these insects, a great multiplica-
tion of tracheae.

On the other hand, in the Trichoptera, Diptera, and most
Hymenoptera, a great reduction of the tracheal system has
taken place. It is not well, therefore, for the student to
begin his studies of this subject with members of either ot
these orders.

In those orders where a specialization of wing- veins by
addition has taken place, the accessory longitudinal veins are
preceded by tracheae.

Finally, it should be remembered that it is not safe to base
conclusions upon the study of a single insect ; a large series,
representing as many genera and families as is practicable,
should be investigated.

CHAPTER VIII

METHODS OF INSECT HISTOLOGY.
INTRODUCTION.

The study of the gross anatomy of most insects requires
no more in the way of equipment than a simple dissecting"
outfit, — viz., scalpels, scissors, needles, and dissecting tray;
and little more in the way of method than skilful manipula-
tion of these simple tools. But for the study of the anatomy
of very small insects, and more especially for the study of
the histology of insect organs, the character of the various
body-tissues, the histolytic and histogenetic phenomena ac.
companying the post-embryonal growth of insects with com-
plete metamorphosis, and, finally, for the study of insect
embryology, a more elaborate equipment is required, and
some knowledge of the special methods of the animal his-
tologist is needed.

Insects present a special problem in histologic method
because of the always present covering of chitin which pro-
tects their bodies. This chitinous wall hinders very effect-
ively the penetration of the fixing fluids and besides presents
very serious difficulties in section cutting. Hence even the
student already familiar with the usual methods of animal
histology needs some special guiding in beginning the study
of insect histology.

The following notes are intended to furnish a guide for
beginning students of insect histology and development.

121

122

.For advanced students, needing a knowledge of more special
methods, Lee's Microtomisfs Vade-Mecum (5th edition, 1900),
and the notes of " technic " given in the many papers treating
of insect histology and development will furnish valuable sug-
gestions. All of the general methods of killing, fixing,
staining, etc., given in the following notes have been person-
ally used by the authors in studying insects. For those few
special cases of treatment of particular tissues and organs
introduced, which have not been tried by the authors, an
authoritative reference to the use of the method is always
given.

It is hardly necessary to say that within certain limits
there is a great deal of difference in the practice of microto-
mists in the matter of method. In these brief notes it is in-
tended to outline a simple, straightforward course of proced-
ure which has been found by actual work on insect tissues to
give good results in such work. Even this plan has been
found difficult to adhere to, because a certain amount of
variation is sure to enter into the practice of any worker.
The student will find out for himself, however, as he gets
more and more familiar with the work, the advantages of
variation, and will be able to take advantage of the oppor-
tunities for modifying his practice presented by the many (at
first glance, confusingly many) suggestions of the standard
manuals of microtomic technic. The following three books
will be of special value for reference.

Lee, A. B. : The Microtomist's Vade-Mecum, 5th edition.
1900.

Whitman, C. O.: Method of Research in Microscopical
Anatomy and Embryology, 1885.

Gage, S. H:; The Microscope, yth edition, 1901.

123

MATERIAL FOR STUDY.

For general histology. — Any organs or tissues desired
for study should be dissected out of a specimen which has
been made insensible by chloroform or ether or cocaine or
which has just been killed by some quick process. The
point is to get the material in a fresh and perfectly normal
condition. The tissue must be alive at the time it goes into
the fixing fluid. A certain way of accomplishing this is to
kill the insect by dropping it into the fixing fluid. But that
the tissue may certainly be reached and affected by the fluid,
the specimen, unless small and with very weakly chitinized
integument, must be cut open.

For studying anatomy or development. — It is often
desirable to make serial sections of the whole body of an in-
sect. In the case of insects too small to dissect this is the
only means of studying their anatomy. In the study of the
post-embryonal development of insects which have complete
metamorphosis, the advanced larval and the pupal stages
must be examined -by such sections, because of the great
breaking down of many of the body-tissues. Specimens
should be killed immediately after moulting, when the outer
chitin wall is thinnest and most pervious to the fixing liquids.
By rearing the specimens, just moulted larvae, just formed
pupae, and just issued imagines may be obtained, and the use
of such specimens will be found to be immensely advan-
tageous. Strongly chitinized specimens, which must be sec-
tioned, may be carefully and cleanly cut into two or three
parts, say, head, thorax, and abdomen. This will enable the
fixing fluids to penetrate the body cavity, although the diffi-
culty of cutting the firm chitin wall with the microtome knife
still remains. Certain methods of softening the chitin are
used by some workers, but there is always danger in the
practice of injuring the other more delicate tissues.

124

For embryology. — In obtaining insect eggs it is highly
desirable, often imperatively necessary, to know the exact
age of the specimens. Hence it is desirable to capture
females of the species to be studied, and if possible have the
eggs laid in captivity. Thus the exact time of oviposition,
and consequently the age of the specimens studied, can be
known. For work simply illustrative of the embryologic
development of insects, eggs should be chosen which are
large, and are not spherical, but of such shape that the speci-
mens can be readily oriented at the time of imbedding or
cutting.

PREPARATION OF MATERIAL FOR SECTIONING.

The sequence of treatment. — The fresh, live mate-
nal (bits of tissue, organs, whole insects, or eggs), which is to
be studied by means of sections, must undergo certain treat-
ment necessary to preserve it, and to prepare it for cutting.
It nas first to be killed and fixed ; next to be hardened ; next
to be cleared ; and finally to be infiltrated with and imbedded
in paraffin (or collodion, see note later). (See also Recapit-
ulation, p. 138.)

Killing and fixing. — Out of the bewildering array of
fixing agents, the student of insect histology must choose a
few which are characterized by great penetrating power.
Many of the commonly used agents for fixing animal tissues
in general cannot be used in work with insects (except where
dissccted-out, non-chitinous organs or tissues are being han-
dled), because of their inability to penetrate the chitinized
integument.

In fixing, a relatively large amount of the fixing agent
should be used, say at least 50 times the volume of the
specimens. The objects should sink, if not at first, then
later, in the fixing fluid. If the objects persist in floating
they probably contain air, and the tissues adjoining air bub-

125

bles will not be fixed. The use of heat as suggested in a
later note may expel the air.

It is our practice to divide our material into at least two
similar lots, three or even four if there are plenty of speci-
mens, and to use a different fixing agent for each of these
lots. For one lot use a sublimate solution, for another a
chromic acid solution, and so on. This not only gives a
variety of fixation, but insures against total loss in the event
of accident to one of the lots.

Boiling water.— 'Drop the live insects into boiling water,
or put them into a glass beaker and pour boiling water over
them. Leave the specimens in the hot water, without further
heating it, for two to five minutes. Then remove to 30$
alcohol for three hours, then to 50$ alcohol for three hours,
then to 70$ alcohol for twelve hours, finally into 85$ alcohol
for keeping. Or the insects may be killed in hot water and
then removed to any one of the fixing agents described in
the following paragraphs. This is probably the best way of
handling whole insects. The method of primarily fixing by
boiling water is especially valuable for eggs and pupae, which,
owing to the impervious character of their chitin-armor, can
hardly be fixed in any other way, but we find that it gives
excellent results in almost all general work.

Picro-aceto-sublimate. — This useful fixing agent is made by
taking of a cold saturated solution of picric acid in 70$ alco-
hol, one part ; of hot saturated aqueous solution of corrosive
sublimate, one part ; and a few drops (]4 to i$) of glacial
acetic acid. The fresh tissue or live insect should be dropped
into this fluid and allowed to remain for from twelve to
twenty-four hours (incline toward the longer time). Remove
to 70$ alcohol for twenty-four hours. (The alcohol will
slowly remove the picric acid, and should be changed two or
three times. If warm alcohol is used the removal of picric
acid will be more speedily accomplished.) Then remove to

126

alcohol, changing once or twice if the alcohol becomes
discolored. It is not necessary to remove all the picric acid
before proceeding to the further preparation of the speci-
mens.

Picro-sulphuric acid. — Distilled water 100 parts, sulphuric
acid 2 parts, picric acid as much as will dissolve. Treat
specimens as for picro-aceto-sublimate.

Mercuro-nitric mixture. — Distilled water, 400 c.c. ; alcohol,
60$ strength, 50 c.c. ; nitric acid, 46$ strength, 7 c.c. ; glacial
acetic acid, 2 c.c. ; corrosive sublimate, 9 grams. Leave speci-
mens in this mixture for from three to twelve hours ; twenty-
four may be better in some cases. Wash in 70$ alcohol and
remove to fresh 70$ alcohol, to which a small amount of
tincture of iodine has been added to hasten the removal of
the corrosive sublimate ; leave in this solution for two or
three days and then transfer to 85$ alcohol for indefinite
keeping.

CJiroino-nitric acid. — Alcohol, 70$ strength, 3 parts ; nitric
acid, iof0 strength, 4 parts ; chromic acid y2% strength, 3
parts. Leave specimens in this mixture four to eight
hours, and wash in 70^ alcohol. Leave in 70$ alcohol for
twenty-four hours, and remove to 85^ alcohol for keep-
ing.

Penetration can be more certainly effected if the fixing
fluid is used warm. Where the killing is done in the labo-
ratory and the fluid can be readily slightly heated, it is well
always to do it.

In addition to the fixing agents of which formulae have
been given, other fixing agents, a host of which are described
in chapters IV. and V. of Lee's Vade-Mecum, may be used.
For cytological work, the osmic acid agents, such as Flem-
niiug's chromo-aceto-osmic acid (Lee's Vade-Mecum, p. 40), and
Hermann's platino-aceto-osmic acid (Lee's Vade-Mecum, p. 45),
should be used.

127

Hardening. — After killing and fixing and washing the
specimens are kept in alcohol of 85$ strength. The speci-
mens may be kept thus indefinitely. Specimens which are
to be prepared for immediate cutting must now be hardened.
(If the specimens are to be stained /// toto, the staining should
now be done before removal to the 95$ alcohol. For direc-
tions, see p. 137.) Remove the specimens to 95$ alcohol
and leave for twenty-four to forty-eight hours, depending
upon size of specimen and degree of chitinization of integu-
ment. Then remove to absolute alcohol for from twenty-
four to forty-eight hours. The specimens, if properly fixed,
will now be thoroughly hardened.

Clearing. — (For theory and practice of clearing, see Lee's
Vade-Mccmn, p. 64 et seq.} Remove the specimens from ab-
solute alcohol to a vial which has been half-filled with xylol
and then filled with absolute alcohol. Put the specimens
into the vial and leave them for twelve to twenty-four hours.
Then remove to a vial filled with xylol and leave them
until cleared. This will require from twelve to twenty-four
hours.

We have used cedar-wood oil a great deal for clearing, as
follows : Remove the specimens from absolute alcohol to a
mixture of absolute alcohol, one part, cedar-wood oil, one
part, for twenty-four hours. Then remove to pure cedar-
wood oil for twenty-four hours.

Chloroform, which has been much used, is rather decried by
the present-day workers. For insects it should be avoided,
as it has little penetrating power.

Infiltrating with paraffin, and imbedding. — After
clearing, the specimens are to be infiltrated with melted
paraffin. The specimens should be removed from the vial
of cedar-wood oil or xylol into a small dish (watch-glass,
beaker, evaporating dish, casserole, tin "pattie" dish), into
which part of the cedar-wood oil or xylol from the vial is

128

poured. Place this dish on top of the paraffin* oven (a
water-bath oven heated at a constant temperature, a little
above the melting point of the paraffin used) and drop into
it several small pieces of paraffin. This paraffin will slowly
dissolve in the cedar-wood oil or xylol and this mixture will
penetrate the specimens. After the paraffin is all dissolved,
add more paraffin and remove the dish to the interior of the
oven. Leave here for from three to six hours, depending on
size, and density, of chitinous integument. Then remove
the specimens to a similar small dish of melted pure paraffin
and keep in the oven for from six to twenty-four hours.
The kind of paraffin to use depends largely upon the charac-
ter of the specimens. For very delicate specimens, a paraffin
of low melting point is desirable. But for most insect work
a hard paraffin is desirable, say paraffin of melting point of
about 55° Centigrade. In the summer, hard paraffin must be
used for the sake of ease in cutting.

Another common method of infiltrating with paraffin is to
remove the specimens from pure xylol or cedar-wood oil to a
mixture (prepared beforehand) of one-half paraffin and one-
half xylol or cedar-wood oil. Leave in this mixture, in the
oven, for from three to six hours, and then remove to pure
melted paraffin and leave, in the oven, for from six to twenty-
four hours.

After the objects are thoroughly infiltrated with pure
paraffin they must be imbedded. Make a small oblong
paper tray (see Lee's Vade-Mecnm, p. 91) and pour into it a
little melted pure paraffin ; when the paraffin has thickened
a little by cooling, so that the objects when put into it will

* The student must get acquainted with the paraffin oven from an inspection
•of that oven which happens to be in use in the laboratory. With much varia-
tion in size, shape, and elaborateness of make, all the different ovens in use
rare essentially simply water-baths with an automatic thermostat for maintaining
a constant temperature.

129

not sink to the bottom and thus have too thin a layer of
paraffin below them, put them in, with more melted paraffin,
and with a warmed dissecting needle arrange them in posi-
tion, i.e., not too near each other, and oriented with regard
to the sides of the paraffin block (that is to be). Cool the
paraffin quickly by floating the tray on cold water (use ice
water in summer), and, as soon as a sufficiently firm film has
formed over the top of the paraffin, by plunging the tray
into the water. In a minute or two the block will be hard
enough to permit of the unfolding and removal of the en-
veloping paper. Leave the paraffin block in the cold water
for ten or fifteen minutes at least, to harden thoroughly.
For very small specimens the imbedding can be done in a
watch glass.

The specimens are now imbedded, and may be preserved
thus indefinitely. On a large piece of paper write a full
label, i.e., name of insect and character of specimen, locality
and date of capture, fixing agent employed, and other de-
tails of preparation that may be valuable to know, and wrap
up the paraffin block in this label. Such labelled and
wrapped up blocks can be conveniently kept in small
wooden or pasteboard boxes, labelled briefly outside with
name of the enclosed specimens.

Instead of paraffin, collodion or celloiclin is sometimes
used for infiltrating and imbedding. It is used especially,
however, for very large objects, />., objects more than one-
half inch in diameter. For small objects paraffin is better
because the sections can be cut thinner. For most insect
work paraffin is far the better medium. (For details of the
collodion method see Lee's Vade-Mecum, p. 120 et seq., and
Gage, p. 157 et seq.)

Section-cutting. — The work of cutting sections with the
microtome can best be learned by the student by seeing such
work done. The differences in construction of microtomes

130

with the varying details of the object-carriers, knife-carriers,
etc., make it impossible to attempt here to instruct the stu-
dent in the details of microtome manipulation.

For cutting insect specimens, especially whole bodies with
their chitinous outer wall, extreme solidity and rigidity of
the microtome in all its parts is absolutely necessary for ac-
curate cutting. The heavy, solidly made, sliding micro-
tomes of the general character of the Thoma-Jung models
are, in our opinion, the microtomes best adapted for general
insect work. The cutting is not done so rapidly as by the
wheel microtomes, but the sureness is an over-balancing item.
Short ribbons, as long as the knife is broad, can be cut with
the sliding microtomes and transferred directly to the slide.

The specimen is cut as a small block out of the larger
paraffin block containing it, and mounted on the object-car-
rier of the microtome. The block to be cut should be rect-
angular in outline, and be set with that margin which will
first strike the knife parallel with the knife. All screw ad-
justments, such as those holding the knife and the object,
should be tightly made, and the block containing the object
should be immovably fastened to the object carrier. The
sections should be, for general work, from 5 microns to 10
microns thick. Except in the case of eggs or delicate tissue,
it is rarely necessary to cut thinner than 5 microns.

The student will undoubtedly meet with more or less
trouble in section-cutting. If it is too warm in the labora-
tory the sections may stick to the knife ; if too cold, they
may roll or break. Rolling of sections is the commonest
trouble in cutting. It is often apparently impossible to get
that proper temperature or condition which will prevent
rolling. There are various expedients for straightening or
hindering the rolling of sections that tend to roll. For
details and suggestions regarding section-cutting, see Lee's
Vade-Mecum, p. 108 et seq.

After the sections are cut, they may, if in ribbons, be kept
on sheets of paper for some time before fastening to the
slides, but it is always advisable for fear of accident whereby
the sections may become lost or disarranged (disarrange-
ment of serial sections is almost as fatal as loss) to fasten
them immediately on to the glass mounting slides.

TREATMENT OF SECTIONS.

The sequence of treatment. — The sections have first
to be arranged and fastened on the s/ide,and have \heparaffin
removed from them ; then they have to be stained, and finally
cleared and mounted. This is the sequence of treatment for
sections which have been cut from a specimen not stained
/;/ toto. If the specimen has been stained before cutting, the
sequence is, (i) arranging and fastening on slide, (2) removal
of paraffin, (3) clearing and mounting. (See also Recapitula-
tion, p. 138.)

In the work of removing paraffin, staining, and clearing
it is necessary that the sections fastened on the slide be
thoroughly bathed by various fluids. The best way of ac-
complishing this is to have the fluids in small glass jars.
These jars should be of a diameter slightly greater than the
width of the slides used and of a height slightly greater
than the length of the slide. They should have closely fit-
ting covers to prevent evaporation, and should be heavy
and firm enough not to be too easily knocked over. The
so-called Naples jars, or the Harvard staining jars, or the
Stender dishes of various dealers are of the proper kind.
Ten or twelve of these jars containing the various necessary
fluids, i.e., xylol, absolute alcohol, alcohol of various
strengths, staining mixture, clearing mixture, etc., properly
labelled, should be arranged on the table in an order corre-
sponding to the successive treatment required by the sec-
tions.

132

Arranging and fastening sections on the slide.—

If serial sections are being cut and the series is long and the
sections of considerable size, larger slides than the ordinary
3 in. by i in. slides can be used to advantage. For most
work, however, the smaller slides do very well. The sec-
tions are to be arranged in regular order in successive lines
either parallel with the short or long axis of the slide as
preferred, leaving uncovered only enough room at one end
of the slide for a suitable label. The rows of sections should
be near together, and the sections near together in each
row, i.e., the paraffin block should, before cutting, be
trimmed as small as is safe. This economizes slides and
covers, and makes the series far more compact and therefore
more readily examined.

Before arranging the sections on the slide, the slide
should be very thinly covered (by rubbing with the finger
tip) with Mayer's albumen fixative (Lee's Vadc-Mecum, p.
143), which can be bought of dealers in microscopical sup-
plies. Then allow a few drops of distilled water from a
pipette to flow over the slide so that the sections may float.
This will straighten out any folded or crumpled sections.
The water must be allowed to evaporate slowly, by putting
the slide on top of the paraffin oven or otherwise heating it
slightly, being careful not to melt the paraffin. After the
sections are entirely dry, the slide should be placed in the
paraffin oven, and allowed to remain until the paraffin is
melted. Or the slide may be gently and carefully warmed
over a gas or alcohol flame. The slide should not be heated
to a temperature higher than required to melt the paraffin.
After the paraffin is melted the slide should be allowed to
cool until the paraffin hardens again.

Removing the paraffin. — The slide should now be put
into a small jar of xylol, which will quickly dissolve the
paraffin. Leave it in the xylol for about ten minutes,, even

133

though the paraffin has apparently been dissolved at the end
of three or four minutes. (The slide can be left in xylol, if
the work must be interrupted, for several hours or even a
day without injury.) Turpentine or toluol can be used in-
stead of xylol. From the xylol remove the slide to a jar of
absolute alcohol (or 96^ alcohol may be used), which will re-
move the xylol. The slide should remain in the alcohol at
least five minutes. It may remain longer without harm. It
should then be transferred to a jar of 90$ alcohol for a few
minutes and then to a jar of 70$ alcohol for a few minutes.
The sections are now ready for staining.

Staining. — The number of different " stains " described
in a manual of technic such as Lee's Vade-Mecum is so large,
and the recommendations regarding their use often so con-
fusing in the uniformity of commendation, that the begin-
ning student of histology is thoroughly at a loss when it
comes to making selection from such an embarras de Hchtsses.
For general work in insect histology there is little demand
for that large and growing series of so-called strictly
chromatin stains, so essential in cytological work. A few
nuclear stains, in the wider sense of the phrase, a few
plasma stains, a stain which will certainly distinguish chitin,
and a stain or two especially for staining in toto, are all that
the beginner needs for most of his work.

Having selected a stain, the student should bring the slide
from the 70$ alcohol (see above) into the jar of staining
fluid. Here the slide must remain until the sections are
thoroughly stained (for time required, see in account of
each stain). Some workers pour a little of the staining fluid
on to the slide, but the use of small jars full of staining
fluid is much to be p'referred. After the sections are
stained, they must be washed in 70$ alcohol or water,
depending upon the character of the staining solution (see
directions in case of each stain). They must then be

134

dehydrated by bathing with alcohol of successive strengths
up to 96$.

The following stains we use commonly and find excellent
for most work : —

FOR STAINING SECTIONS.

Mayer's acidulated carmine (Lee's Vade-Mecum, p. 174). —
Carminic acid, 4 grams, distilled water, 15 c.c., hydrochloric
acid, 30 drops. Boil till the carmine is dissolved, and after
cooling add 95 c.c. of alcohol of 85^ strength (or for stain-
ing /';/ toto use alcohol of 95$ strength), and filter the fluid.
After filtering, the now acid solution should be made neutral
by slowly adding drops of ammonia until neutralization is
effected. This gives a beautiful, deeply-red-coloired, and
quickly acting stain. Leave the slide in the stain from five
to fifteen or twenty minutes. Remove to 70$ alcohol for
washing and then to 96$ alcohol. It will be noted that, in
addition to the sections, the thin coating of albumen fixative
on the slide has been slightly stained. This can be removed
by passing the slide quickly through 96$ alcohol containing
a very little (i to 1000) hydrochloric acid. This bath of
acidulated alcohol also " differentiates " the stain, i.e., takes
out some of the stain from the cytoplasm of the cells, leav-
ing the cytoplasm much more faintly stained than the nuclei.
From the acidulated alcohol the slide should be removed to
pure g6fc alcohol. (For further manipulation see Clearing
and Mounting, posted.}

Grenadiers alcoholic borax-carmine (Lee, p. 172). — Make a
concentrated solution of carmine in borax solution (2 to 3
per cent, carmine to 4 per cent, borax) by boiling for half an
hour or more ; dilute it with about an equal volume of 70$
alcohol, allow it to stand 24 hours and filter. Add to this
solution an equal amount of 70$ alcohol ; allow the mixture

135

to stand for a week and again filter. Especially useful for
Staining in bulk.

Delafield's hamatoxylin (Lee, p. 184). — This is one of the
long used standard stains and can be bought, ready pre-
pared, of any dealer in microscopical supplies. The formula
for its making is as follows : " To 400 c.c. of saturated solu-
tion of ammonia alum (ammonia alum dissolves in about n
parts of water) add 4 grams of haematoxylin crystals dis-
solved in 25 c.c. of strong alcohol. Leave it exposed to the
light and air in an unstoppered bottle for three or four days.
Filter and add 100 c.c. of glycerin and 100 c.c. of methylic
alcohol (CH4O). Allow the solution to stand until the color
is sufficiently dark, then filter and keep in a tightly stop-
pered bottle. ... It should be allowed to ' ripen ' for at
least two months before using it." (Lee.) For staining,
some of this stock solution should be considerably diluted
with distilled water. We add a few drops of acetic acid (fol-
lowing Biitschli's suggestion) and get a much sharper stain.

The color is blue, but the acetic acid produces a strong
reddish tinge. As this is an aqueous stain, the slide should
be carried from the 70^ alcohol (see p. 133) to a jar of dis-
tilled water before putting it into the jar of staining fluid.
The stain acts quickly, depending on the amount of dilu-
tion, and should be washed out with water. After washing
with water, the slide should be carried through 50$, 70$, and
into 96^ alcohol. It does not need differentiation (if acetic
acid has been added) and the albumen coating does not take
up the stain.

Mayer 's hcemalum (Lee, p. 182). — One gram of hsematein
dissolved with heat in 50 c.c. of 90$ alcohol, and added to a
solution of 50 gr. of alum in a litre of distilled water. Allow
the liquid to cool and settle, and filter if necessary. A
quickly acting stain. After staining, the sections should be
washed in distilled water.

136

Picric acid. — If desired, and it will often be advisable, to
follow the nuclear stain (any one of the preceding) with a
secondary stain, picric acid can be employed to best advan-
tage. It is of special value in insect histology because it
clearly distinguishes chitin. A little picric acid should be
added to a small jar of 96$ alcohol and the slide passed
through it before going into the pure 96$ alcohol. This
bath of picric alcohol must come after the bath of acidulated
alcohol used in differentiating after Mayer's acidulated car-
mine.

Heidenhains iron hcematoxylin (Lee's Vade-Mecum, p. 189).
This is a more complicated method of haematoxylin staining,
which, however, gives excellent and beautiful results and is
very helpful in those cases where cellular structure is being
studied. The staining is done as follows : Put sections for
from one to two hours in a 2% to 4$ aqueous solution of fer-
ric alum (NH4)sFea(SO4)v This mordants them. Then
wash the sections in water for from five to ten minutes.
Then stain for from one-half to two hours in a yz% aqueous
solution of haematoxylin (made by taking 3 c.c. of a 16$
alcoholic solution of haematoxylin, chloral hydrate 2 grams,
and distilled water 97 c.c.). Then wash the sections in
water, and differentiate by dipping the slide for a few sec-
onds in the mordant (the ferric alum solution) and then
rinsing in tap water, repeating this operation until the cor-
rect differentiation has been attained as ascertained by ex-
amination of the wet slide under the microscope. The
chromatin should be deep blue or blue black, the cytoplasm
gray or light blue. After differentiating, the slide should be
washed in running water for fifteen or twenty minutes to
remove completely the ferric alum. Considerable practice is
necessary to obtain the best results with this stain. It
should not be used with thick sections, i.e., thicker than 10
microns, for it is an opaque stain.

137

FOR STAINING IN TOTO.

If it is desired to stain the insect specimens before cutting
the sections, a custom which used to be very commonly fol-
lowed, but is being discarded by many present-day workers,
a very penetrating stain must be used. Perhaps the most
widely used stain of this character is Grenadier's alcoholic

*

borax-carmine (see p. 134) This stain, all. ready for use, can
be bought of any dealer in microscopical supplies. The
specimens, pieces of tissue or organs, or small insects with
weakly chitinized integument, are taken from the 70^' alco-
hol in which they have been kept for a day after fixing (see
pp. 125, 126) and are put into this stain and left there for
one or two clays or even longer, and then put into 70$ alco-
hol which has been acidulated with hydrochloric acid (i
HC1 to 1000 alcohol) for differentiation. Leave the speci-
mens in the acidulated alcohol until no more coloring mat-
ter is being extracted. Then wash in neutral 70^ alcohol
and harden in 85$, 95^, and absolute alcohol, clear, imbed,
cut, and after removing the paraffin from sections in xylol
(see p. 132) mount in balsam (see below).

Mayer's acidulated carmine (see p. 134) can also be used
for staining in bulk as well as for staining sections.

Clearing and mounting. — The sections after staining
and washing and removal to 95$ alcohol have yet to be
cleared and mounted. Either cedar-wood oil or xylol or
other similar oils may be used We use xylol commonly.
The slide should go from the 95'^' alcohol into a jar of abso-
lute alcohol for ten or fifteen minutes and then into a jar of
xylol for as long a time. For mounting use thin balsam and
no more than is necessary. The xylol is very volatile and
the mounting must be done rapidly to prevent a drying of
some of the sections. This is an accident to be carefully

133

avoided throughout the whole course of manipulation. If
the sections dry they are most likely ruined.

After mounting, put the slides into the paraffin oven for
several hours to harden the balsam. The label should bear
not only the name of specimen but, advisably, the name of
stain used and also the name of fixing agent. The date of
mounting should be added, so that the sections may serve as
tests of the value of the method of fixing and staining.
Some stains do not hold well when used after certain fixing
agents.

RECAPITULATION.

As a convenient guide for the beginning student the
course of procedure described in the preceding pages is here
recapitulated in its proper sequence.

FOR MATERIAL TO BE STAINED IN SECTIONS ON SLIDE.

1. Kill and fix fresh material with fixing agent (p. 124).

2. Wash out fixing agent with 70$ alcohol (pp. 125, 126).

3. Remove to 85;";' alcohol for keeping, or for beginning
hardening (pp. 125, 126).

4. Harden in 95^ alcohol and absolute alcohol (p. 127).

5. Clear in xylol, cedar-wood oil or other clearer (p-
127).

6. Infiltrate with paraffin in paraffin oven (p. 127).

7. Imbed (p. 1 28).

8. Cut sections (p. 129).

9. Fasten sections on slides with Mayer's albumen and
water (p. 132).

10. Remove paraffin from sections with xylol or other
agent (p. 132).

11. Remove xylol with absolute alcohol (p. 133).

12. Carry through 90^ alcohol and 70^ alcohol (p. 133).

139

13. Stain with Mayer's acidulated carmine, Mayer's haem-
alum, or other stain (p. 133).

14. Wash out stain with 70$ alcohol, or water if aqueous
stain is used (p. 133).

15. Remove to 95$ alcohol (p. 134).

16. Differentiate with acidulated 95$ alcohol (p. 134).

17. Remove to neutral 95$ alcohol (p. 134).

18. Remove to absolute alcohol (p. 137).

19. Clear sections with xylol, cedar-wood oil, or other
clearer (p. 137).

20. Mount in balsam.

21. Label.

22. Harden balsam mounts in paraffin oven.

FOR MATERIAL STAINED IN TOTO.

Vary the preceding course of procedure as follows :
Between 2 and 3 stain in toto with alcoholic borax carmine,

or other stain (p. 137)

Omit 12 to 18 inclusive. (It is possible to mount directly

after removing paraffin with xylol, but the mount is likely

to be unclean unless fresh xylol is used for removal of the

paraffin.)

INDEX AND GLOSSARY

Abdomen (ab-do'men), 8, 27-

Accessory glands, 42.

Accessor}- veins, no.

Ad, the ending, 2.

Adipose tissue (ad'i-pose), 35, 56.

Albumen fixative, 132.

Alcohol, acidulated, 134, 137.

Alimentary canal, 36, 56.

Anal angle, 95.

Anal furrow, 94.

Anal prolegs, 33.

Anal veins, 90.

Angles of wings, 95.

Anosia plexippus (A-no'si-a plex-

ip'pus), 84.

Antecoxal piece, 24, 71.
Antennae (an-ten'nae), 13.
Antennal nerves, 50.
Antennal sclerites, I~J.
Antennary fossa, 13.
Ant-lions, wings of, 115.
Anus (a'nus), 30.
Aorta (a-or'ta), 47.
Apex of the wing, 95.
Apis rnellifica (A'pis mel-lif'i-ca), 77.
Arculus (ar'cu-lus), 92.
Areas of the wing, 93.
Asilid (As'i-lid), wing of an, 98.
Aspects of appendages, 5.
Aspects of the body, 4.
Attachments of the alimentary canal,

37;

Auditory organs, 28.

Basiproboscis, 84.

Bleaching wings, 99.

Blood-vessels, 47.

Boiling water, 125.

Bombyliid (Bombyl'i-id), wing of a,

98.

Braconid (Brac'o-nid), wing of, 108.
Branched suspensory muscle, 38.
Branched veins, 88.

Bullas, 94.

Bursa copulatrix, 45.

Cardinal directions, the six, 2.

Cardo (car'do), 15.

Carmine, 134.

Caudad (cau'dad), 2.

Caudal (cau'dal), 2.

Celloidin, 129.

Cells of the wings, designation of

the, 92.

Cephalad (ceph'al-ad), 2.
Cephalic (ce-phal'ic), 2.
Cerci (cer'ci), 28.
Cervical sclerites, 12, 20.
Chauliodes (Chau-li'o-des), wings of,

"5-

Chitin (chi tin), 8.

Chloral hydrate, 32.

Chromo-nitric acid, 126.

Cicada (Ci-ca'da), 80.

Clearing, 127.

Clypeal (clyp'e-al) suture, 64.

Clypeo-frontal suture, 17.

Clypeus (clyp'e-us), 11.

Colleterial (col-le-te'ri-al) gland, 44,

46.

Collodion, 129.
Compound eyes, 9.
Confluent, 69.

Construction of the terms used, 2.
Corydalis cornuta (Co-ryd'a-lis cor-

nu'ta), 31 ; wings of, 106.
Cossid (Cos'sid), wings of a, 101.
Costa (cos'ta), 89.
Costal margin, 95.
Coxa (cox'a), 26.
Coxal cavities, 68.
Cross-veins, 88, 91.
Crura cerebri (cru'ra cer'e-bri), 51.
Crus, 51.

Cubitus (cu'bi-tus), 90.
Culex, wing of, 99.

141

142

Delafield's hasmatoxylin, 135.

Dichotomous branching of veins, 112.

Digitus (dig i-tus), 67.

Uiptera, wing-veins of, 97.

Distad (dis'tad), 4.

Distal (dis'tal), 4.

Distiproboscis, 84.

Dolichopodid (Dol-i-chop'o-did),

wing of a, 98.
Dorsad (dor'sad), 2.
Dorsal (dor sal), 2.

Ectad (ec'tad), 4.

Ectal (ec'tal), 4.

Egg-calyz, 43.

Egg-guide, 29.

Egg-tubes, 4).

Ejaculatory duct, 40.

Elytra (el'y-tra), 72.

Embryology, material for study of,

124.

Empidid (Em'pi-did), wing of an, 98.
Entad (en'tad), 4.
Ental (en'tal), 4.
Entire, by.

Epicranial suture, 17.
Epicranium (ep-i-cra'ni-um), 10, 64.
Epimeron (ep-i-me'ron), 24.
Epipharynx (ep-i-phar'ynx), 18, 85.
Epipleura (ep-i-pleu ra), 68, 72.
Episternum (ep-i-ster'num), 22, 24.

Fastening sections on slide, 132.

Fat, 35, 56.

Femur (fe'mur), 26.

First, second, third, etc., 5.

Fixative, 132.

Fixing T 24.

Ylabellcm (fla-bel'lum), 79.

Flemming's chromo-aceto-osmic

acid, 126.

Frenate moths, wings of, 101.
Frenulum (fren'u-lum), 99.
Frenulum hook, 102.
Front, 1 1 .

Frontal ganglion, 51.
Frontal ridge, 64.
Furcula (fur'cu-la), 28.
Furrows of the wing, 94.

Galea (ga'le-a), 15.

Ganglia (gan'gli-a), 34.

Gastric caeca (gas'tric cse'ca), 36.

Genae (ge'nae), 1 1.
Generalized, 87.
Glossa (glos'sa), 19, 67.
Grenacher's borax carmin, 134.
Great-dorsal-recti-muscles, 53.
Great-ventral-recti-muscles, 53.
Gula (gu'la), 65.
Gular (gu lar) sutures, 66.

Haemalum, 135.

Haemal oxylin, 135, 136.

Hardening, 127.

Head, 7.

Head, parts of the, 9.

Heart, 47.

Hepialus (He-pi'a-lus), wings of,

101.
Hermann's platino-aceto-osmic acid,

126.

Histoblasts, 61.

Histology, methods of insect, 121.
Holorusia rubiginosa, 54-
Honey-bee, wing of, 108.
Humeral angle, 95.
Humeral cross-vein, 91.
Hymenoptera, wings of, 102.
Hypopharynx (hy-po-phar'ynx), 14,

20, 77.
Hypothetical type of wing. 96.

Ichneumon-fly, wing of, 108.
Imaginal buds, 6l.
Imbedding, 127.
Infiltrating, 127.
Inner margin, 95.
Intermediate, 6.
Interrupted, "]?..
Intestinal caecum, 57.
Intestine, 37, 56.
Intima (in'ti-ma), 46.
Iron haematoxylin, 136.

Jugular sclerites (ju'gu-lar scle'rites),

13-

Jagum (ju'gum), 101.

Killing, 124.

Krauss, Dr. William C., 51.

Labella (la-bel'la), 84.
Labial palpi (la'bi-al pal'pi), 14.
Labium (la'bi-um), 14.
Labrum (la'brum), II

Lacinia (la-cin'i-a), 15.
Laterad (lat er-ad), 2.
Lateral (lat'er-al), 2.
Lateral filaments, 33.
Legs, 26.

Lepidoptera, wings of, 99.
Ligament of the viscera, 39, 42.
Ligula (lig'u-la), 14, 20.
Limitations to accuracy, 6.
Locusts, 7.

Longitudinal veins, 88.
Lora, 79.
Lyonet, 51.

Macroxyela (Mac-rox"y-e'la), 103.
Malpighian vessels (Mal-pe'ghi-an

or Mal-pig'hi-an), 36, 56.
Mandibles (man di-bles), 13.
Mandibular scrobe, 66.
Margins of wings, 95.
Masticatory organs of the proven-

triculus, 39.

Maxillae (max il'lae), 13, 15.
Maxillary palpus (max'il-la-ry pal'-

pus), 1 6.

Maxillary segment, 17.
Maxillary tendons, 84.
Mayer's acidulated carmine, 134.
Mayer's albumen fixative, 132.
Mayer's hsemalum, 135.
Media (Me'di-a), 90.
Medial cross-vein, 92.
Median furrow, 94.
Medio-cubital cross- vein, 92.
Mediproboscis, 84.
Melanoplus femur-rubrum (Me-lan'o-

plus fe'mur-ru'brum), 7.
Mentum (men'tum), 14.
Mercuro-nitric mixture, 126.
Mesad (mes'ad), 3.
Mesal (mes'al), 3.
Meson (mes'on), 3.
Mesonotum (mes-o-no'tum), 21, 22.
Mesosternellum, 24.
Mesosternum (mes-o-ster'num), 23.
Mesothorax (mes-o-tho'rax), 22.
Metanotum (met-a-no'tum), 21, 22.
Metasternellum, 24.
Metasternum (met-a-ster'num), 24.
Metathorax (met-a-tho'rax), 22.
Micropyle, 45.
Monarch Butterfly, wings of the,

101.

Mounting sections, 137.
Mouth parts of a locust, I£,

of a butterfly, 84.

of a cockroach, iS.

of a cicada, 80.

of the honey-bee, 77-

ot a hornet, 75.

of the horse-fly, S2.

of the house-fly, 83.
Musca domestica, 83.
Muscid, wing of a, 98.
Muscles, 51.

Nervous system, 50
Neuroptera, wings of, 108.
Nodal furrow, 95.
Numbering of wing-veins, 90.

( >blique lines, 3.

Obsolete, 9.

Occiput (oc'ci-put), 11.

Ocelli (o-cel'li), 9.

Ocellus (o-cellus), 9.

OZsophagus (oe-soph'a-gus), 36.

Ommatidium (om-ma-tid 1'i-um), 9,

Open, 69.

Optic nerves, 51.

Outer lobe, 15.

Outer margin, 95.

Ovaries, 41, 43, 46, 58.

Oviduct (o'vi-duct), 29, 41.

Ovipositor (o-vi-pos'i-tor), 28.

Palpifer (pal'pi-fer), 15.
Palpiger (pal'pi-ger), 14.
Pamphilius (Pam-phili-us), 103.
Paraffin, infiltrating with, 127.
Paraffin, removing, 132.
Paraglossae (par-a-glos'sse), 19, 67.
Patagia (pa-ta'gi-a), 99.
Penis, 42.

Pericardial diaphragm, 48.
Peritremes (per'i-tremes), 24.
Pharynx (phar ynx), 36.
Picric acid, 136.
Picro-aceto-sublimate, 125.
Picro-sulphuric acid, 126.
Pleurite (pleu rite), 28.
Pleurum (pleu rum), 28.
Plica (pli'ca), 72.
Podical (pod'i-cal), plates, 28.
Postgenae (post-ge'nae), 12.
Postmedia (post-me'di-a), 90.

144

Postscutellum (post-scu-tel'lum), 21.
Prsescutum (Pras-scu'tum), 21.
Premedia (pre-me'di-a), 90.
Preservation of specimens, 32.
Prolegs, 33.

Pronotum (pro-no'tum), 21.
Propygidium (pro-py-gid'i-um), 73.
Prosternellum, 22.
Prosternum (pro-ster'num), 21.
Prothorax (pro-tho'rax), 21.
Proventriculus (pro-ven-tric'u-lus),

36.

Proximad Cnrox'im-ad), 4.
Proximal (prox'i-mal), 4.
Pseudotracheae (pseu-do-tra'chese),

84.
Pterostichus californicus (Pte-ros'ti-

chus cal-i-for'ni-cus), 63,
Pulvilli (pul-vil'li), 26.
Pygidium (py-gid'i-um), 73.

Radial cross-vein, 91.

Radial sector, gb.

Radio-medial cross-vein, 91.

Radius (ra'di-us), 89.

Recti muscles, 53.

Rectum, 37, 57.

Removing paraffin, 132.

Reproductive organs, 40.

Respiratory system, 46.

Rhyphus (Rhy'phus), wing of, 87.

Rolling of sections, 130.

Salivary glands, 57.

Scenopinid (Sce-nop i-nid), 98.

Sclerites (scle'rites), 8.

Scutellum (scu-tel'lum), 21, 23.

Scutum (scu'tum), 21, 23.

Section cutting, 129.

Seminal vesicles, 42, 46.

Sequence of treatment of material,

124.
Setigerous (se-tig'er-ous) punctures,

,.65-

Sialis (Si a-l;s), wings of, 115.

Simple eyes, 10.

Simple suspensory muscle, 38.

Simple veins, 88.

Siricid (Si-ric'id), wing of, 108.

Small -dorsal-recti-muscles, 53.

Specialization by addition, 109.

by reduction, 109.
Specialized, 87.

Spermatheca (sper-ma-the'ca), ^4,
Spermatozoa (sper'ma-to-zo'a), 43.
Sphecid, wing of, 108.
Spiracles (spir'a-cles or spi'ra-cles>,

. 24, 57-

Spurious vein, 99.

Sternite (ster'nite), 28.

Sternellum, 21.

Sternum (ster'num), 21, 28.

Stigma, 103.

Stipes (sti'pes), 15.

Stomach, 36.

Stylets, 82.

Subcosta (sub-cos'ta), 89.

Subcostal fold, 94.

Subgalea (sub-ga'le-a), 66.

Submentum (sub-men'tum), 14.

Suboesophageal ganglion (sub-oe-

soph-ag'e-al), 51.
Superior lobe, 15.
Supraoesophageal ganglia (su-pra-oe-

soph-ag'e-al), 50.
Suspensoria (sus-pen-so'ri-a), of the

viscera, 37.

Suspensory muscles, 38.
Suspensory nerves of 'the alimentary

canal, 39, 49.
Sutures (sfit'urs), 9.
Sympathetic nervous system, 59.
Syrphid, wing of a, 98.

Tabanid, wing of, 98.

Tabanus (Ta-ba'nus), 82

Taenidia (tae-nid'i-a), 47.

Tarsus (tar'sus), 26.

Technical nomenclature, need of

a, I.

Tegmina (teg'mi-na) 27.
Tenthredinids (Ten"thre-din ids,

wings of), 108.

Tentorium (ten-to'ri-um), 12, 17.
Tergite (ter'gite), 28.
Tergum (ter'gum), 28.
Testes, 40, 41, 46.
Testicular follicles, 40.
Thorax (tho rax), 8; parts of, 2O.
Tibia (tib'i-a), 26.
Tipulid, 54.

Tracheae (tra'che-ae), 46.
Tracheal gills (tra'che-al), 33.
Tracheation of wings, 117.
Trochanter (tro-chan'ter), 26.
Trochantin (tro-chan'tin), 211.

145

Tympanum (tym'pa-num), 28.
Typical branching of the wing-veins,

95-

Upper lobe, 15.

Vagina, 41.

Vagus nerve (va'gus), 51.

Vasa deferentia (va'sa def-e-ren'ti-a),

40.

Vas deferens (vas def'e-rens), 40.
Venation of the wings, 86.
Ventrad (ven'trad), 2.
Ventral (ven'tral), 2.
Ventral diaphragm, 49.
Ventriculus (ven-tric'u-lus), 36.
Vertex (ver'tex), II.
Vespa maculata, 75.

Ward, the suffix, 2.
Wing-covers, 27.
Wings, 27.
Wings of the heart, 48.

of ant-lions, 115.

of an Asilid, 98

Wings of a Bombyliid, 98.

of a Braconid, 108.

of Chauliodes, 115-

of Corydaiis, 115.

of a Cossid, 101.

of Culex, 99.

of Dolichopodids, 98.

of an Empidid, 98.

of frenate moths, IOI.

of Hepialus, lol.

of a Honey-bee, 108.

of Hymenoptera, IO2.

of an Ichneumon-fly, Io8.

of Lepidoptera, 99.

of the Monarch butterfly, 101,

of a Muscid, 98.

of Neuroptera, 108.

of Rhyphus, 87.

of Scenopinid, 98.

of Sialis, 115.

of a Siricid, 108.

of a Sphecid, 108.

of a Syrphid, 98.

of a Tabanid, 98.

of Tenthredinids, 108.
Wing-veins, 86.