One family, the Phlaeothripidae, is recognized in the suborder Tubulifera, whereas extant species of Terebrantia are classified into seven families : Uzelothripidae, Merothripidae, Aeolothripidae, Adiheterothripidae. Fauriellidae (stat. n.), Heterothripidae and Thripidae. A phylogenetic analysis of the relationships between these families is given, based o n consideration of 35 imaginal characters; however, the relationships of Uzelothripidae and Phlaeothripidae to the rest of the Thysanoptera remain equivocal. The Phlaeothripidae are either derived independently from Protothysanoptera, or else are the sister-group of the Thripidae, the most specialized family of Terebrantia.Diagnostic characters, diversity, distribution and relationships of each family are discussed. Keys to family and, in Fauriellidae, to genus are provided. Holarthrothnps Bagnall (= Adihetrrothrips Ramakrishna, syn. n.) and Oligothrips Moulton are removed from Heterothri idae to Adiheterothripidae and Fauriclla Hood, Opisthothrips Hood and Ropotamothrips Pefikan (= Osmanothnps Priesner, syn. n.) from Heterothripidae to Fauriellidae (stat. n.). These transfers leave Aulacothnbs Hood, Heterothrips Hood and Scutothrips Stannard as the only genera in Heterothripidae.

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During the propupal and pupal stages of Frankliniella fusca and Haplothrips verbasci, each leg consists of coxa, femur, and tibiotarsus.The adult pretarsus, tarsomeres, and tibial gland of F. fusca arise during the pupal stage through morphogenesis of the distal tibiotarsal epidermis. These structures become functional at the time of adult emergence on the completion of cuticle deposition. Most leg epidermal cells degenerate soon thereafter.The imaginal tarsal depressor muscle develops during the pupal and pharate adult stages through fusion and differentiation of myoblasts originating elsewhere in the body. Myofibrils of the larval pretarsal depressor muscle disappear during the propupal stage but reappear during the pupal and pharate adult stages with a different, adult configuration.At the larval–propupal apolysis, the larval restraining tendons detach at both ends from the larval cuticle, contract, and, throughout metamorphosis, nestle between the epidermis of unguitractor apodeme and tibiotarsus. During the pupal stage the tendons rotate transversely 90° and grow laterally through addition of new material to their sides.In H. verbasci, completion of these events requires an additional pupal stage.Leg metamorphosis in thrips is compared with that occurring in other insects and additional remarks are made on the origin of holometabolism in Thysanoptera.Chez la pronymphe et la nymphe de Frankliniella fusca et d'Haplothrips verbasci, chaque patte est constituée d'une coxa, d'un fémur et d'un tibio-tarse.

Structure and Function of the Mouthparts in Larvae ofHaplo th rips ve rba sci (0 s bo r n> (T h y sa no p t e r a, Tu bu I if era, P h laeo t hr i pidae) B. S. HEMINGDepartment ofEntomology, UniuersityofAlberta, Edmonton, Alberta, Canada T6G 2E3 ABSTRACTWhen a larva of Haplothrips verbasci is ready to feed, it grasps the surface of the leaf with its pretarsi, sinks down between its front legs, lifts its head, and places the tip of its mouthcone against the surface. It then shortens its mouthcone and punches a hole in the epidermis by rapidly and repeatedly protracting and retracting its left mandibular stylet. The thrips then inserts its two maxillary stylets as a unit into the wound with a series of rapid thrusts and withdrawals, salivating continuously while doing so. When a food source in the epidermis or mesophyll is found, probing and salivation stop and cibarial pumping begins. Cytoplasm is sucked into the opening a t the tip of the protracted stylets, up the food canal between them and into the cibarium.Probing and feeding can occur without mandibular intervention but uptake of liquid seems to require use of the mutually coadapted maxillary stylets, even when these are fully retracted.Prior to molting, the larva protracts its maxillary stylets maximally and, in the pharate state, seems incapable of feeding or drinking.Structures used in feeding are fully described and are shown to resemble those of Hemiptera except for the presence of maxillary and labial palpi and the absence of the loral lobes, right mandible and of a salivary canal between the protracted maxillary stylets. Seven single and 18 paired muscles function in the feeding act, nine less than in adults of the same species.Differences in the feeding mechanism of terebrantian and tubuliferous thrips are discussed and evidence is presented to suggest that the simplified and more highly specialized mouthparts of the latter insects are adaptations for feeding in confining spaces.

Comparison of germ cells in male and female embryos of the arrhenotokous thrips, Haplothrips verbasci, yields the following observations: A mean of 11 cleavage energids enter the posterior pole plasm of the egg after the sixth cleavage division and apparently become pole cells when they take up polar granules in their cytoplasm. The cells proliferate asynchronously prior to and during anatrepsis to yield a mean of 36 germ cells in male embryos and 31 in females. Visible sexual differentiation of germ cells begins during germ band elongation and is completed shortly after the appearance of appendages. Female germ cells are larger than those of the males and may contain two nucleoli. The germ cells separate into two groups just before katatrepsis and mesodermal cells collect about these to form the primary epithelial sheaths of the gonads and the primordia of the gonoducts shortly after revolution is completed. Each gonad contains a mean of 13 germ cells in male embryos and 7 in females - a number that persists until mitosis resumes after hatching. During ketatrepsis, a mean of 11 germ cells in male embryos and 2.6 in females fail to be enclosed within the gonads, become dispersed in the yolk and perhaps transform into vitellophages. Germ cell development in H. verbasci embryos resembles similar events taking place in psocid embryos, providing additional evidence for a close phylogenetic relationship between Thysanoptera and Psocoptera.

Newly deposited eggs of Rhodnius prolixus lack a visible pole plasm and require 14 days to develop at 27 °C and 70% RH. The first germ cells originate at 9% of embryogenesis by asynchronous mitosis of blastodermal cells behind the germ Anlage at the posterior pole of the egg. From 9 to 17%, these proliferate to a mean of 270 cells and, from 13 to 18%, migrate forward over the dorsal surface of the mesoderm and lodge in abdominal segments 3–7. Between 22 and 30%, they shift laterally and segregate into three or four paired clumps between segments 3 and 4, 4 and 5, 5 and 6, and, sometimes, 6 and 7 and, from 30 to 37%, gradually assemble into a continuous longitudinal mass on either side of segments 3–6, where they begin to associate with mesodermal cells. Between 37 and 46%, these collect between (males) and around the germ cells to form the rudiments of the terminal filaments (females), inner and outer gonadal sheaths, interstitial cells (males), and primary exit ducts. Dorsally situated sheath cells then invaginate ventrally into each gonadal rudiment, partitioning it into seven compartments, each containing a mean of 15 oogonia or 16 spermatogonia. These seem to fuse into a rosette, at least in females, but do not begin to divide again until after hatch. Excluded germ cells lodge within the rudiments of one or both exit ducts. The evolutionary and functional aspects of our findings are addressed and new observations are presented on the mechanism of anatrepsis.

The functional morphology of the unique pretarsal mechanism of adult Thysanoptera is described. The components of each pretarsus are homologous with those of other insects, but changes in their relative sizes and shapes have arisen through modifications in their function. Among these are the enlargement of the arolium into a protrusible bladder; the reduction of the ungues into spoon-shaped, laterally ensheathing plates; the development of a tibial gland opening to the surface of the arolium through three fine ducts; and the evolution of two elastic "restraining" tendons each inserting into the "head" of the unguitractor apodeme and originating laterally on the walls of the distal end of the tibia.The contraction of the pretarsal depressor muscle causes the ungues to rotate outward on the unguifer and blood pressure, increased by abdominal contraction, everts the arolium. When the depressor muscle relaxes, the restraining tendons contract and the arolium is withdrawn between the closing ungues by sclerites and filaments associated with each. The adults of species in all five families of the order have this mechanism.

At hatching (252-264 hr. at 25 k 0.5"C), the visual system in larvae of Lytta uin'dana consists of paired stemmata, stemmatal nerves, optic neuropiles, and inner and outer imaginal optic lobe anlagen. I t originates between 64 and 72 hr. with invagination of an optic lobe primordium in the side of each protocephalic lobe. These primordia later differentiate into protocerebral ganglion cells and the imaginal optic lobe anlagen. Each stemma arises at 72 hr. from epidermis below and behind the optic lobe invagination and subsequently becomes cupshaped, closes over, and differentiates. At hatching, it consists of a planoconvex corneal lens, a corneagenous layer, and an everse retina of numerous, pigmented retinular cells, each with a terminal rhabdomere. Between 96 and 104 hr, proximal ends of the retinular cells grow posteromedially into a transverse, horizontal fold in the posterior wall of each optic lobe invagination and along its length to the protocerebral neuropile, which they contact by 112 hr. As the brain withdraws posteriorly within the head, these axons elongate correspondingly. Sheath cells of stemmata and stemmatal nerves descend either from protocerebral perineurium or the optic lobe primordia. Structure and development of the larval visual system in L. uiridana are cornpared with those of other insects and its various components are shown to be homologous throughout the Insecta. However, the stemmata of this insect more closely resemble the atypical imaginal eyes of male scale insects than the photoreceptors of other holometabolous larvae -a similarity arising through convergence.In detailed studies of several species of holometabolous insect, the compound eyes and optic lobes of adults have been shown to differentiate respectively from previously determined eye-disc cells in the larval head and from optic lobe anlagen in the protocerebrum of the larval brain during postembryogenesis (reviews of