The basic anatomy of phasmatids has been outlined in works by Littig (1942), Beier (1957), and Key (1970). A phasmatid is morphologically a very simple orthopteroid insect; the general body-form is elongate, slender, and cylindrical, although occasionally the body may be depressed and broadened. Many stick-insects have the body ornamented with swellings, spines or foliaceous expansions.
The phasmatid head is elongate to almost globular in shape and is usually prognathous, although in some forms with a swollen vertex, it appears hypognathous. The head may be ornamented with spines or tubercles, and the vertex may be swollen and bear spines or elongate horns. The antennae are inserted on the front of the head and vary in length from much shorter than the anterior femora to longer than the whole body. The scape is short and generally dorsoventrally compressed, but it may be cylindrical. The pedicel varies from globular to cylindrical. The flagellomeres are usually elongate and cylindrical; the articulations between the articles are sometimes difficult to discern. The compound eyes are laterally placed and prominent, even though they are not as large as in the true Orthoptera. Ocelli, if present, are arranged in a triangle on the front of the head. The mouthparts are adapted for chewing and are uniform throughout the phasmatids. The mandibles are strong and well-sclerotized. The maxillae have 5-segmented palps, 2-segmented galeae, and dentate laciniae which bear bristles on their inner surfaces. The labium has 3-segmented palps and well-developed paraglossae and glossae, with the latter being slightly smaller.
The thorax is elongate with no fusion of segments to form a pterothorax and no development of the pronotal plate to form a saddle-shaped shield as in the true Orthoptera. The prothorax is elongate and rectangular, but, in some cases can be broader than long. The anterolateral angles of the pronotum may have openings for a defensive gland; in some instances, this gland appears to be atrophied (Moxey, 1971), and some genera have no defensive gland. The mesothorax is the longest thoracic segment; its notum is usually convex. Tegmina, if present, arise from the hindmost part of the mesonotum. The metanotum is similar in form to the mesonotum, and in some apterous species is greatly elongated. Abdominal segment I is closely associated with the metathorax, its sternum being reduced, and the tergum fused with the metanotum. [In Timema Scudder, abdominal tergite I is free from the metanotum, and there is a distinct notal-tergal suture; the sternum, however, is reduced as in other phasmatids.] The notal-teral suture is represented only by a groove in the sclerite; the area caudal to this groove is called the median segment.
Phasmatid limbs are gressorial and thus are long and slender; often they are armed with spines or foliaceous lobes. The coxae are small and well-separated. The trochanter, a small segment between the coxa and femur, is unremarkable. The anterior femora are usually strongly curved and somewhat compressed basally; because of this, the femora can accommodate the head when they are held forward in an outstretched manner. Some forms, such as Taraxippus Moxey, have the head placed sufficiently above the horizontal plane of the legs that the anterior femora can be aligned under the head; in these, the femora are not basally curved. The posterior four tibiae often have the lower carinae armed with strong spines. These tibiae, and sometimes the anterior pair as well, may have a depressed triangular area on the median aspect (the “areolate” condition). In the others, the lower median carina runs to the apex, or, if the carina is absent, the distal tibia shows no depressed area (the “anareolate” condition). The tarsi are 5-segmented. The first article is often elongated, sometimes dorsally sulcate or crested. [Timema Scudder appears to have 3-segmented tarsi; in this case, the first three tarsomeres are fused dorsally, but the pulvilli are separated ventrally.] The tarsi of regenerated legs have only four tarsomeres. Terminal claws and an arolium are present.
Phasmatids may be apterous, exhibit varying degrees of brachyptery, or have full hindwings. In the alate state, the forewings are small tegmina which, at rest, usually cover only the bases of the hindwings; for this accommodation, the tegmina have a knob-like elevation in their basal half. The hindwings are broad and divided into two areas:  a narrow, tough remigium and a large anal-fan. Wing-venation is fairly uniform throughout the group (Ragge, 1955).
The abdomen has eleven segments and is dorsoventrally compressed to cylindrical. The first segment is fused with the metathorax. [Many of the older systematic works on the Phasmatodea did not include the “median segment” in the numbering of the abdominal segments. In this work, I call the first free segment behind the posterior coxae “abdominal segment II.”] Tergum X is well-developed; tergum XI is concealed beneath tergum X in the male, but in the female, it is usually visible and occasionally elongate—the supraanal plate. Sternum VII of the female often has a praeopercular organ. Sternum VIII in the female is elongate, scoop- or keel-shaped, and is called the subgenital plate (=operculum, auct.). In the male, the subgenital plate is sternum IX, the distal lobe of which is usually swollen and cup shaped (=poculum, auct.). Sternum X may be modified to have a posteriorly-directed acuminate sclerotized process, the vomer. Cerci are unsegmented, usually short and simple; sometimes in the male, they may be large and strongly-curved, used for clasping the female during copulation.
The morphology of the genitalia has been described by Pantel (1915), Chopard (1920), Snodgrass (1937), and Snodgrass (1957). Abdominal sternite VII of the female is often modified for receiving the male vomer during copulation (the praeopercular organ). Hidden underneath the female subgenital plate is the 3-valved ovipositor. Male sternite X may be modified to have a posteriorly-directed acuminate sclerotized process, the vomer. Phasmatid male genitalia may be useful taxonomic characters for suprageneric classification; within genera, however, they are extremely uniform, showing little, if any, variation between species. The external genitalia have four asymmetrical, usually membranous, valves, two dorsal and two ventral, surrounding the gonopore. The valves may have strongly-sclerotized areas, especially near their bases; the two dorsal valves may unite, thus making the gonopore ventral. The now-single dorsal valve often has a sclerotized plate giving it support. The two ventral lobes tend to develop small finger-like projections around the gonopore; the ventrodextral lobe may have a small lateral sclerite bearing a moveable sclerotized hook. A second type of male genitalia has only a single, thick and cylindrical phallic structure for the genital opening. In this type, the phallus is apically divided into short right and left lobes, with a small median lobe.
The eggs of the stick-insects are large and most-remarkable in their resemblance to seeds. The shape of the egg is oval or cylindrical; the outer shell is very hard, its texture ranging from smooth-and-shining to rough-and-heavily-sculptured. At the truncated anterior pole of the egg is the operculum (=cap, auct.) through which nymphs emerges. Laterally, there is a longitudinal scar-like area called the micropylar plate; this region contains the micropylar opening through which sperm enter the egg for fertilization.