1,721,173 research outputs found
Ricerche sui Collemboli XXVIII. Su di una nuova specie endogea di Schaefferia.
No full textViene descritta la nuova specie Schaefferia scossirolii. La specie è caratterizzata dalla presenza di 3+3 occhi e 6+6 setole sui Denti. Gli esemplari sono stati ottenuti da campioni di terreno di un campo coltivato localizzato nei dintorni di Caserta
Recenti acquisizioni sulla struttura e funzione dell'apparato riproduttore femminile di Ceratitis capitata
No full textL'apparato riproduttore femminile di Ceratitis capitata è stato studiato sia dal punto di vista strutturale che biochimico e biomolecolare. In particolare, si è messo in evidenza che la secrezione delle ghiandole accessorie può giocare un ruolo chiave nel processo riproduttivo. I risultati ottenuti appaiono promettenti per il controllo "biologico" dell'insetto attraverso l'utilizzazione di metodiche biomolecolari sul processo riproduttivo
The sperm glycocalyx of Pezotettix giornai (Rossi) (Insecta: Orthoptera) after quick-freeze, deep-etching
No full textMature spermatozoa of the catantopid orthopteran Pezotettix giornai are characterized by an elaborate external glycocalyx. This coating is removed during storage in spermatheca allowing preparation of sperm to their interaction with female gametes. We have studied this membrane coating in mature sperm by both conventional transmission electron microscopy and quick-freeze, deep-etching. The ultrastructural studies allowed visualization of three different domains in glycocalyx of testicular and deferent duct spermatozoa and only two in sperm cell isolated from seminal vesicles. These observations thus demonstrate that a remodeling of the male germ cell starts already during their storage in the seminal vesicle and is completed in the female genital tract. In this paper a three-dimensional (3D) model of sperm external coating is presented and discussed
A molecular approach for studying the biology of the olive fly (Bactrocera oleae): mitochondrial genomics and microsatelliti loci
No full textThe ultrastructure of Malpighian tubules and hindgut of Frankliniella occidentalis (Pergande)(Tisanoptera, Thripidae)
No full textThe ultrastructure of the western flower thrips, Frankliniella occidentalis (Pergande) (Order: Thysanoptera), has 4 Malpighian tubules that are free of the intestine as they leave their junction at the pyloric region. The tubules consist of an epithelium with a single type of microvillated cells; proximally, the cells are lined by a thin cuticle. Numerous mitochondria, basal infoldings of the plasma membrane and vesicles with varying densities suggest active transit of fluid in the cell for osmoregulation. Two of the Malpighian tubules are bent posteriorly and closely adhere to the hindgut in the region of the rectal pads where the 2 epithelia are separated only by a basal lamina. The ultrastructure of this region suggests possible fluid reabsorption from the gut lumen
The ultrastructure of the spermatheca in Ceratitis capitata Wied and Dacus oleae Gmel (Diptera: Tephritidae)
No full textThe spermatheca of two economically important insects, Ceratitis capitata and Dacus oleae (Diptera, Tephritidae) was studied by scanning and transmission electron microscopy.
The organization of this organ is very similar in both species: it consists of an apical receptacle where spermatozoa are stored and a long duct opening in the vagina. The apical receptacle is characterized by a secretory epithelium structured as in insect ectodermal glands, lined by a cuticular intima. The secretory cells have an asynchronous secretion cycle, more evident in Ceratitis capitata.
Two types of secretions have been observed in Ceratitis: one has a microtubular appearance, the second is glycoprotein in nature.
The spermathecal duct consists of two ultrastructurally distinct parts: the distal one shows cells with microtubular bundles anchored to the opposite sides of the cell membrane; this organization is able to resist to mechanical stress during the transport of spermatozoa. The proximal tract of the duct is characterized by cells involved in osmoregulatory functions
Aberrant spermatogenesis and the peculiar mechanism of sex determination in Symphypleonan Collembola (Insecta)
No full textLight and electron microscopy evidence have been obtained to describe the peculiar spermatogenesis in the collembolan species Sminthurus viridis and Allacma fusca (Sminthuridae), In these two species, the two sexes differ for the lack of two chromosomes (the sex chromosomes) in males (males, 2n = in; females, 2n = 12), While oogenesis seems to proceed normally, spermatogenesis is peculiar because the two daughter cells of the first meiotic division have different chromosome numbers (six and four). The cell receiving four chromosomes degenerates, while the cell receiving six chromosomes completes meiosis and produces identical spermatozoa (n = 6), At fertilization, pronuclei with six chromosomes fuse together to form zygotes with 2n = 12, Male embryos must lose two sex chromosomes during the first zygotic mitosis, as all male cells have 2n = 10 chromosomes. The sex chromosome system of these species can be identified as X1X1X2X2:X(1)X(1)0. Electron microscopy observations show that the same peculiar spermatogenesis occurs also in two others species of the same family, Caprainea marginata and Lipothrix lubbocki, The peculiar sex determination system described is similar but not identical to what is observed in other insect orders, and it may represent an evolutionary step toward parthenogenesis, It is suggested that this peculiar spermatogenesis is common to all Symphypleona
The spermatozoon of Arthropoda. VI. Ephemeroptera
No full textIn this work the spermatozoon of Chloëon dipteron (Ephemeroptera) is examined. The three most important features are that (a) the acrosome is very brief; (b) the mitochondrial derivative is represented by a long mitochondrion with transverse cristae and by a crystalline mass enveloped in a separated membrane; (c) the axial filament of the tail lacks the two principal central units and the central sheath, and is therefore, of the 9 + 9 +0 pattern. This type of flagellum has not previously been described. © 1969 Academic Press, Inc
New data on the aberrant spermatogenesis of Collembola
No full textAberrant spermatogenesis in the two species Stenognathellus denisi (Katiannidae) and Sminthurides aquaticus (Sminthurididae) is described. An ultrastructural study of spermatogenesis in these species has allowed us to reveal the presence of two types of secondary spermatocytes; one with a normal appearance, the other one is characterized by a small size, a reduced cytoplasm (showing only two centrioles), and a nucleus with very condensed chromatin. These latter aberrant cells are not able to perform the second meiotic division and will degenerate. This finding allows us to extend the identification of an aberrant spermatogenesis and the consequent postzygotic sex determination to two more families of Symphypleona
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