Post‐Embryonic Development of the Female Genitalia and of other Structures in the Chalcidoid Insect Harmolita graminicola Gir.

Abstract

Summary. The female genitalia and the oviducts and their attendant glands are shown to arise from three pairs of imaginal discs or buds situated on the seventh, eighth, and ninth abdominal segments.The pair on the seventh abdominal segment are shown to form the oviducts and basal region of the female sexual organs; the pair on the ninth abdominal segment become reduplicated to form two pairs of appendages, which, together with the pair of buds on the eighth abdominal segment, form the gonapophyses of the ovipositor.Stages are shown prior to and after the formation of the second pair of buds on the ninth abdominal segment, and it is quite conclusive from my sections that both pairs of buds originate in the same segment, the inner pair being formed from the outer pair. The metamorphic changes of the alimentary canal are described in some detail. The two long, larval, salivary glands are the first structures to begin degenerating, and they have, in large part, disappeared before the pupal stage is reached. The anterior region of each gland persists and forms the basis of certain of the salivary glands in the adult. The malpighian tubes persist longer than the salivary glands, and are still present when the imaginal malpighian tubes can be detected. They disappear, however, before pupation takes place.Degenerative changes appear to take place in the gut by a kind of lyocytosis, as no phagocytic action was observed. The epithelial lining becomes vacuolated and finally disintegrates into the lumen of the gut to form material for the integration of the adult tissues, which process proceeds simultaneously.Important formative areas were found at the junction of the larval œsophagus and mesenteron and at the latter's junction with the small intestine. Although the continuity of the gut is maintained throughout the metamorphic changes, the re‐constitution of the fore‐ and hind‐gut proceeds far more rapidly than that of the mesenteron. In a seven‐day old pupa the external appearance of the gut approximates to that of the adult, but internal histological changes are not completed until the pupal stage is far advanced. The ventral nerve‐cord of the larva is of a fairly generalised nature. It consists in both sexes of a brain and subœsophageal ganglion, three thoracic ganglia, and eight abdominal ganglia, the last of which is compound, being a fusion of three ganglia. There is little difference in appearance between the male and the female ventral nerve‐cords until the metamorphic changes begin, and then variations are most marked in the abdominal region. The first two abdominal ganglia in both sexes fuse with the metathoracic ganglion instead of only one abdominal ganglion, as is more common in other Hymenoptera. In the female the compound or last abdominal ganglion becomes the second abdominal ganglion in the adult. The first abdominal ganglion in the adult female is formed from the fusion of the third, fourth, fifth, sixth, and seventh larval abdominal ganglia. In the male all the larval abdominal nerve‐masses, except the first two, fuse to form the only abdominal ganglion to be found in the adult. The cutaneous musculature is of a fairly simple nature, consisting essentially of a segmental arrangement of an equal number of dorsal and ventral longitudinal muscle‐bands, with pairs of lateral and ventral oblique muscles on all the segments except the cephalic and the last body‐segments. The only muscles of importance in the cephalic segment are those which move the mandibles.The cutaneous muscles are not attached to the hypodermis but are inserted directly on to the cuticle.The larval musculature is destroyed by phagocytosis near the time of the pupal ecdysis. The larval dorsal vessel possesses three chambers, while that of the imago possesses five. Whether the latter is an entirely new structure or a modification of this organ in the larva the writer was unable to ascertain. A detailed account is given of the various imaginal discs and other formative areas found in the larva, including the rudiments of the antennae, the compound eyes, mouth‐parts, legs, and wings.Generally speaking, each body‐segment may be said to possess four undifferentiated masses of formative tissue, except in those segments where they have been differentiated to form the imaginal discs of the wings, legs, or genital structures. The respiratory system of the larva possesses a hitherto unrecorded type of closing apparatus. Its essential feature is the presence of three opposable chitinous pads in a somewhat constricted region of the wall of a stigmatic branch. This constricted region of the tube is surrounded by a sphincter muscle, whose contraction causes the chitinous pads to occlude the lumen of the tube, and thus close the spiracle. There is no atrium. The young pupa possesses the same type of closing apparatus, but that of the imago is of quite a different type.