1,721,033 research outputs found
Oogenesis in kalotermes flavicollis (Fabr.) (isoptera: Kalotermitidae).ii. prefollicular and follicular cell ultrastructure during oogenesis in female supplementary reproductives
No full textOvariole somatic cells were examined by light and electron microscopy. Prefollicular, follicular and interfollicular cells were identified. Prefollicular cells envelop oogonia and oocytes at the beginning of meiosis; they have a scarcely differentiated cytoplasm with protrusions penetrating between germ cells and between these and the tunica propria. Follicular cells form a flattened epithelium around initial previtellogenic oocytes, and during previtellogenic growth they proliferate and change from flattened to cuboidal and then columnar shape. They adhere tightly to each other and apically form microvilli which extensively interlock with oocyte microvilli. During vitellogenesis, the follicular cells show a globose shape; wide intercellular spaces appear between adjacent cells and between follicular cells and the oocyte. Their cytoplasm becomes enriched in rough endoplasmic reticulum cisternae, Golgi complexes, mitochondria and microtubules, particularly near the basal area. At the end of vitellogenesis the follicular cells are flattened and very wide, and earlier intercellular spaces have disappeared. From the last previtellogenic stages to the end of oocyte development, the ovarian follicles are separated by interfollicular cells anchored to the tunica propria and characterized by the present of numerous microtubules in the cytoplasm. The function of the ovariole somatic cells is discussed in relation to the stages of oocyte differentiation and growth
Preliminary observations on endocellular bacteria in the ovaries of Kalotermes flavicollis (Fabr.)(Isoptera, Kalotermitidae)
No full textIn electron microscopic studies on the oogenesis of neotenic queens of Kalotermesflavicollis, we found bacteria both in cytoplasm and nuclei of germ cells (oogonia and oocytes in alI developmental stages) and in follicle cells. Similar bacteria were occasionally seen in sheath cel1s of the ovary. The bacteria appear elongate, approximately, 150 nm and 45 nm wide. Their outside boundaries are the plasmalemma, an intermediate layer, and another double membrane, externally wrapped by a host cell membrane. Internally a fibrous matrix is found with ribosomes
Oogenesis in Kalotermes flavicollis (Fabr.) (Isoptera, Kalotermitidae). III. Choriogenesis and corpus luteum formation in female supplementary reproductives
No full textFollicular cell ultrastructure during chorion and corpus luteum formation was studied in supplementary reproductives of the termite Kalotermes flavicollis. During choriogenesis the follicular epithelium is formed by large flattened cells joined together by specialized junctions. Follicular cells have an extended rough endoplasmic reticulum (RER) with cisternae parallel to the cell long axis and many Golgi complexes surrounded by secretion vesicles moving towards the egg surface. At the end of choriogenesis the follicular cells move away from the just completed chorion and show few RER cistemae and scarce Golgi apparati. When the egg is ejected from the ovariole, the empty ovarian follicle collapses; the irregularly shaped follicular cells, now exhibiting in their cytoplasm small autophagic vacuoles and polymembranous structures, form the initial corpus luteum. This undergoes a further shrinking, becoming an ovoidal mass (the advanced corpus luteum) formed by irregularly shaped follicular cells containing numerous heterogeneous inclu- sions. The ultrastructural evidence rules out any hint of a functional activity of corpus luteum cells, but supports the hypothesis of their progressive degeneration. The chorion is made up of an endochorion with a trabeculate structure and a compact layer exocho- rion. The chorion surface is sculptured with polygonal plates which are follicular cell imprints. On the egg dorsal side, near the posterior pole, there is the micropylar region formed by several oval plates arranged in an arched pattern. On the same side, near the opposite pole, the preformed field for embryo hatching is found, made up of four rows of rectangular plates
Oogenesis in immature stages and sterile castes of Kalotermes flavicollis (Fabr.) (Isoptera: Kalotermitidae
No full textOvaries of winged and dewinged imagos, 2nd instar nymphs, pseudergates, presoldiers and soldiers of Kalotermes flavicollis were investigated. During the normal developmental cycle, after the imaginal moult, the ovary starts to produce eggs as a result of the activation of oogenic processes. In pseudergates, presoldiers and soldiers oogenesis is blocked at the first previtellogenic stage and the oocytes undergo degeneration. In nymphs a block is also observed, but it happens at the second previtellogenic stage and without any hint of oocyte degeneration. The evidence suggests that in pseudergates, presoldiers and soldiers, the oogenesis block is related to a lack of differentiation of follicular cells which may be one of the main targets for control factors.
Preliminary observations on endocellular bacteria in the ovaries of Kalotermes flavicollis (Fabr.)(Isoptera: Kalotermitidae)
No full textUltrastructural study of testis development and spermatogenesis in kalotermes flavicollis (Fabr.) (isoptera, kalotermitidae)
No full textTestes of larvae, nymphs, young winged imagoes and primary reproductives of Kalotermes flavicollis (Fabr.) were examinep by light and electron microscopy. They are composed of 7-8 lobes enveloped by a tri-layered wall made up or: i) an outer monolayered cellular sheath above an acellular lamina; ii) a lacuna in which plasmatocytes and granulocytes are found; iii) a testis tunica propria. In the 3rd and 4th larval instar it is not yet possible to discriminate the somatic cells from the germ ones. In the 5th- instar larvae, lobes exhibit the typical organization of insect testis follicles with four, linearly arranged regions. In the germarium a group of apical cells, in close connection to predefinitive primary spermatogonia, is present- In 5th instar larvae, spermatogenesis is completed and, in the testis terminal chamber, sperms are always found. In nymphs, young winged imagoes, and primary reproductives, all regions of testis follicles appear progressively larger than 5th instar ones and cysts of germ cells are more numerous. Germ cell ultrastructure during spermatogenesis is mostty similar to the one described far other insect species, but distinctive features of K. flavicollis, reported here far the first time, are: i) in the cytoplasm of definitive primary spermatogonia and secondary spermatogonia, the presence of a «cisternal complex» made up of a bunch of smooth endoplasmic reticulum cisternae, which disaggregates in primary spermatocytes; ii) the presence of microvillar expansions on the surface of secondary spermatogonia and primary spermatocytes; iii) the loss of syncytial arrangement during the first meiotic division, which ls associated to the loss of synchronous development within a cyst
Preliminary observations about ovaries in soldiers, pseudergates and nymphs in Kalotermes flavicollis (Fabr.) (lsoptera: Kalotermitidae).
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Preliminary observations on spermatogenesis in immature stages and fertile and sterile castes of Kalotermes flavicollis (Fabr.) (Isoptera: Kalotermitidae)
No full textTestes of larvae, nymphs, primary reproductives, pseudergates and soldiers of K. flavicollis were investigated with light and electron microscope. In the course of male gonad morphogenesis, at the apex of the testis lobes an apical tissue differentiates and persists even in the imago. In larvae, up to 4th instar, the lobes are made up of morphologically similar cells in which a distinction between somatic and germ cells is not possible. During transition from 4th to 5th larval instar, the lobes acquire the typical structure of the follicle testes of insects. In primary reproductives, the testes are voluminous and all four regions with peculiar patterns of germ cells differentiation increase their size. In pseudergates, nymphs and soldiers, although the stages of spermatogenesis and spermiogenesis are found, testes do not reach the size, structure and fully functional state of primary reproductives
Osservazioni sulla morfogenesi del testicolo in Kalotermes flavicollis(Fabr.) (isoptera: Kalotermitidae)
No full textIn K. flavicollis, nell'intervallo che intercorre tra i due ultimi stadi larvali, il testicolo si modifica radicalmente: i) i lobuli acquisiscono l'organizzazione strutturale tipica dei follicoli degli insetti; ii) viene attivato il processo spermatogenetico; iii) le cellule della, linea germinale divengono morfologicamente riconoscibili da quelle della linea somatica. Questa serie di modificazioni risulta negli insetti piuttosto inconsueta, poiché le cellule germinali sono normalmente distinguibili già durante lo sviluppo embrionale ed i follicoli mostrano l'inizio della organizzazione testicolare fin dai primi stadi larvali
Ovary and testis development in different stages and in the caste of Kalotermes flavicollis (Fabr.) (Isoptera Kalotermitidae)
No full textThe structure of gonads during normal development and in the sterile caste of Kalotennes flavicollis (Fabr.) was studied using light and electron micro- scope. The typical organization of the ovary is acquired between the 2nd and 3rd larval stage, and by the testis between the 4th and the 5th stages. Ovary development gradually advanced to the 5th larval stage; in 1st and 2nd stage nymphs, presoldiers, soldiers and pseudergates, oogenesis is blocked at the beginning of previtellogenesis with terminal oocyte degeneration. After the imaginal moult, terminal oocytes begin to store yolk. Spermatogenesis up to mature spermatozoa is already completed at the 5th larval stage. Mature spermatozoa are also observed in the testes of 1st and 2nd stage nymphs, presoldiers, soldiers and pseudergates. The testis reaches a maximum size and is fully functional in reproductives through an extensive recruitment of secondary spermatogonia
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