However, metamorphosis produces major changes in the integument, the muscles of the head and abdomen, the digestive tract, the fat body, and the tracheal system. According to Whedon (1929), dissolution of the larval abdominal muscles is not completed until several days after molting.
THE HEAD
Nothing is known of the early odonate larvae, but when they took to the water their first concern must have been to develop some means of aquatic respiration. As some modern zygopterous larvae have lateral gills along the sides of the abdomen, and in this respect resemble the larvae of mayflies, we may reasonably suppose that the primitive odonate larvae were first equipped to breathe in water.
6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 1 23 At the time when the aeschnid imago is ready for ecdysis, the larval
THE FEEDING APPARATUS
8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I23 jaws lying horizontally in the space between the labrum and the hypo-
Both mandibles of Anaxareus are the same size and shape, have the same dentition and. Maxillae.— Larval maxillae are typical generalized maxillary appendages except for the absence of galeal lobes ( Fig. 3C ). The thin outer lobe {C,Plp) is sometimes regarded as a galea, but the fact that it has two basal muscles (E) indicates that it is.
In the retracted position (A,Mx) the cardines are folded dorsally above the stipites, where they are articulated on the cranial edge (C,a') just in front of the posteriortentorial pits. The sclerotic lateral walls of the pit are continuous superiorly with the hypopharynx itself, and meet ventrally below the salivary orifice to form a V, from which a large T-shaped or anchor-shaped apodema arises posteriorly (Fig. ^). h,hAp). The apodemal support clearly corresponds to the fulcrum arch of the hypopharynx of a cockroach, and the apodema is merely a continuation of it.
A pair of long, slender muscles (A, E, 20) arise from the process on the lower surface of the apodeme, which enter the labium and insert at the base of the prementum (Fig.
10 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I23 of the cockroach that go from the hypopharyngeal fulcrum to the
NO. 2 DRAGONFLY LARVA — SNODGRASS II
The abductor muscles of the palpi (fig. 5A, 46) lie entirely within the prementum, as in other insects, but the large adductor muscles (^7) break all the rules of labial anatomy by originating in the distal end of the postmenum. The postmentum is supported in the membranous ventral wall of the head behind the maxillae (Fig. 3A, Pmf). Thus, the true hinge points of the labium on the head are located at the tips of these rods, where the rods meet the basal lobes of the postmentum (Figs. 3A, 5 B,/i).
They are placed on the prementum anterior to the elbow hinge (A, F, 20) and act as flexors of the prementum on the postmentum. The somewhat thicker muscles of the second pair (A, E, 44) arise on the tentorium {Tnt) and are placed on lever-like arms (F,/w) of the premental base which project beyond the elbow hinge; these muscles are therefore effective extensors of the prementum. Thus in theodonate larvanospecial muscles have been developed for the unusual movements of the labium on the head.
A special group of muscles not represented in other insects is present in the elbow region of the larval labium, there are two of these muscles on each side (Fig. 5G).
NO. 2 DRAGONFLY LARVA — SNODGRASS 13
14 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL, 1 23
NO. 2 DRAGONFLY LARVA — SNODGRASS 15
In these larvae the labium is relatively smaller than in an anisopterous larva, and the narrowness of the abdomen may compensate for the absence of a diaphragm. A next step must have been to lengthen the postmentum into a movable stem, giving the prementum greater reach in its new role. Therefore, an accessory mechanism had to be developed to allow the labium to swing at the base of the postmentum.
Finally, then, evolution provided a hydraulic mechanism by which blood pressure could be applied against the soft membrane of the neck behind the base of the postment and cause the latter to oscillate. Perhaps primarily the blood pressure is created by the contraction of the anterior abdominal muscles and pectoral muscles, but this provides a greater effect. Along with the development of the labial mechanism, the head necessarily underwent an adaptive modification.
Now the question arises, how should we visualize the development of a complex mechanism such as the nutritional ap-.
NO. 2 DRAGONFLY LARVA SNODGRASS 1
SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I23
NO. 2 DRAGONFLY LARVA — SNODGRASS 1
THE ALIMENTARY CANAL
20 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I23 chamber should be referred to the colon, and that the end chamber
THE THORAX
NO. 2 DRAGONFLY LARVA — SNODGRASS 21
22 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I23 to facilitate their use as organs for entrapping flying prey on the wing,
The most important internal changes that take place in the thorax relate to the completion of development in the wing muscles, although there. Maloeuf (1935) showed that the muscles of the larval thorax are of two types: large, striated functional muscles, which are mostly the muscles of the legs; and slender, unstriated non-functional muscles, which are the prospective wing muscles. The wing muscles, says Maloeuf, "grow greatest in fiber number and diameter during the time of the final transformation." The muscular attachments undergo little change during transformation, although "the skeletal parts to which they are attached may be greatly changed.
The growth of the muscle cells and the multiplication of fibrils ends with the beginning of the imaginal stage. The thoracic musculature of the adult anisopterous dragonfly has been shown by Clark (1940) to comprise essentially the same muscles as are present in the thorax of other insects, including direct and. Also in cockroaches, mantids and termites the back muscles are small or absent, but these insects have not developed a motor mechanism for the wings from the other muscles to any degree comparable to that of the dragonfly.
24 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL, 123 says of the mature anisopterous thoracic musculature that it is “highly.
24 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL, 1 23 says of the adult anisopterous thoracic musculature that it is "highly
THE ABDOMEN
Since the narrow anterior end of the branching chamber can be closed by the ileal valve, the water can be discharged by impacting the chamber itself. Again, the water is sometimes kept in the chamber and stirred or churned for better aeration of the gills. Kauatmung of Tonner), The three small circumanal lobes between the bases of the apical processes of the larva (Fig. 11 G) apparently actasan anal lobe; in live larvae they can be seen actively opening and closing.
The ordinary respiratory movements of the bronchial chamber as seen through the body wall are precisely synchronous with the dorsoventral and transverse expansions and contractions of the abdominal wall itself. On the other hand, when the water is forced out from the anus, and the larva suddenly leaps forward with its legs extended behind the body, it is to be seen that with each impulse the abdomen contracts lengthwise posteriorly. Abdominal tergal plates are simple, strongly convex arches with slightly prominent lateral edges (fig. 9F).
The median sternites are almost of uniform width throughout the length of the abdomen (A), but the laterosternites are very small on the anterior segments (J) and largest on the middle part of the abdomen.
26 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 1 23
The lateral muscles include external, intrasegmental, vertical tergosternal muscles (C, F,/^) in each segment, and a long oblique intersegmental muscle (lo) from the lateral side of each tergumin front to the laterostenite of the posterior segment. In most segments the fibers of the external lateral muscles are grouped on either side in two thick bundles attached to the side of the tergum and inserted on the inner edge of the laterosternite, but in the anterior segments the fibers are fewer. Finally, in addition to the segmentally repeated muscles, there are the muscle dia-. phragma of the fourth segment {B,Dph), the transverse muscle of the sixth segment (tmcl), and in the tenth segment special muscles of the apical lobes.
The breathing movements of the larva are most pronounced in the wider posterior half of the abdomen. Expiratory muscles are therefore the lateral muscles attached to the inner margins of the laterosternites. During inspiration, lateral muscles relax, the tergal arch is restored, the sternum descends and resumes ventral convexity (F).
He therefore accepted and elaborated on the idea of Matula (1911) that the inspiratory movements are mainly caused by contractions of the diaphragm and the transverse muscle.
28 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I23 of these muscles rhythmically brought the cut edges of the back to-
The main propulsive force exerted on the inflated respiratory chamber is therefore apparently due to contraction of the ligaments of the dorsal and ventral intersegmental muscles. These muscles, as already noted, are highly developed in the larva, but are completely lost after transformation to the adult, demonstrating that they are of functional importance only in the larval stage. However, it is possible that the transverse muscle and perhaps the diaphragm assist in the expulsive contraction of the abdomen.
Since the modern anisopterous and zygopterous larvae are mainly differentiated in their mode of respiration, the question naturally arises how the primary odonate larva achieved respiration when it first entered the water. Yet some means of breathing in the water must have been the first adaptation necessary for an insect when it adopted an aquatic life. 34;We have good reason to look upon Cora and its allies as being in many respects the most primitive of living Odonata." It is therefore not impossible or improbable that the primary odonate larva developed tracheal gills along the sides of the abdomen, and that in this in this respect resembled the larvae of the modern mayfly.
The tail appendages of young zygopterous larvae are slender processes, which according to Tillyard (1917) become triquetral in the second or third instar, and become flattened in subsequent instars.
30 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I23 ing lateral abdominal gills ( D ) the caudal appendages are large vesicu-
NO. 2 DRAGONFLY LARVA SNODGRASS 31
32 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I23 abdomen is wholly destroyed with the transformation to the imago,
The three tapered horny lobes surrounding the anus of the anisopterous larva (Fig. 11 F) appear superficially to correspond to the epiproct and paraprocts of. Dorsal to the sides of the middle lobe are a pair of smaller appendages (Cer) which have exactly the relative position of the usual abdominal cerci. In the transformation of the male anisopterous larva to the adult, the "cercoids" become the superior prehensiles (fig. loE,F, C^r), the dorsal anal lobe (Eppt) becomes the so-called "inferior" prehensiles.
It seems incredible that these lateral plates in the adult can be cerci; they have the exact position of the paraprocts relative to. These processes of the paraprocts have been shown by Asahina (1949) to be of unusual size, though only slightly sclerotized, in both the male and female of the anisozygopteron Epiophlebiasuperstes. In an adult anisopterous female, the end of the abdomen (Fig. 10G) is so typically orthopteroid that it might fit a grasshopper or locust.
The apical appendages of zygopterous larvae, either of the broad lamellar form (Fig. 11 A) or of the slender triquetral type (B), are supported on basal plates (A, Eppt, Papt) which are apparently the true epiproct and paraprocts.
SUMMARY
2)6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 1 23
A phylogenetic study of the terminal abdominal structures and male genitalia of Apterygota, ephemerids, Odonata, Plecoptera, Neu-.
38 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I23 Pflugfelder, O
