摘要:

AbstractThe abdominal intersegmental molting muscles ofRhodnius prolixusundergo a repeated differentiation and dedifferentiation correlated with the molting cycle of the insect. In the dedifferentiated phase, the muscle fibers lack myofibrils but contain a few bundles of 50–60Å filaments associated with amorphous dense plaques on the sarcolemma. Differentiation of the muscle fibers begins when a starvedRhodniusnymph takes a blood meal. The first morphological signs of differentiation at ten hours after feeding are a dispersal of ribosomes from the nuclear envelopes and a formation of polysomes in the sarcoplasm. The initial myofilaments appear within 10 to 15 hours after the blood meal and are preferentially deposited in the cortices of the muscle fibers in association with the 50–60Å filament bundles and the dense plaques on the sarcolemma. Striated myofibrils are present after five days of differentiation. Developmental continuity between Z‐band segments and sarcolemmal dense plaques is suggested. The formation of cross‐bridges between thick and thin myofilaments appears to be the primary mechanism of myofibril organization. Disruption of microtubules with colchicine does not significantly alter myofilament deposition and organization during early stages of differentiation. Dyads, consisting of smooth sarcoplasmic reticulum and invaginations of the sarcolemma, are present in the dedifferentiated muscle fiber, and increase in number as differentiation

ISSN:0002-9106    

DOI:10.1002/aja.1001240102

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1969

数据来源: WILEY

摘要:

AbstractParts of the medial and lateral habenular nuclei were removed unilaterally in each of thirteen opossums and the brains were studied for fiber degeneration by a modified Nauta method. Degeneration was seen in the ipsilateral, but not the contralateral, habenulopeduncular tract, which at the level of the interpeduncular nucleus underwent a partial decussation over it, whereas there were almost no degenerating fibers in the nucleus itself. Caudal to the nucleus extensive degeneration was present bilaterally among nuclei of the raphé and this extended into the predorsal fasciculus. Many terminals were observed in the nuclei of the raphé and within the deep tegmental nucleus. Although degenerating fibers were seen in the region of the dorsal tegmental nucleus, no terminals could be identified with certainty. Degeneration was also present in the superior colliculus.Bilateral degeneration occurred in the stria medullaris and extended to the preoptic area and the olfactory tubercle. In the dorsal preoptic area a small, but quite definite fiber bundle, separated from the posterior surface of the stria medullaris, traversed the lateral hypothalamus and passed dorsal to the mammillary bodies into the midbrain tegmentum, where it became intermingled with fibers of the habenulopeduncular tract just ventral to the red nucleus.Findings appear to indicate that in the opossum relatively few, if any, fibers of habenular origin terminate in the interpeduncular nucleus. In addition, fairly substantial evidence has been obtained to show that there are a number of efferent fibers within the stria medullari

ISSN:0002-9106    

DOI:10.1002/aja.1001240103

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1969

数据来源: WILEY

摘要:

AbstractThe gestation period ofTadaridais approximately four months long extending from late February to June. During the first half of gestation the yolk sac undergoes a complete collapse bringing two layers of endodermal cells into contact with one another and obliterating the cavity of the yolk sac. Both the endodermal and the mesodermal cells hypertrophy and develop into a glandular‐looking organ during the latter half of gestation. Approximately a month before parturition the endodermal cells become progressively laden with lipid and glycogen. Immediately before birth, however, both of these storage materials are depleted. This depletion is preceded by the formation of an extensive array of hexagonal membranous channels within the cytoplasm. Some of the membranes of this organelle are closely applied to lipid droplets and glycogen granules can be observed in linear patterns within the hexagonal channels. Tissues taken at term showed the membranes of the hexagonal channels continuous with a paracrystalline membranous structure. The close morphological association of the membranous organelle to both the lipid and glycogen storage materials indicates that it is involved in their metabolism in the yolk sac of the ba

ISSN:0002-9106    

DOI:10.1002/aja.1001240104

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1969

数据来源: WILEY

摘要:

AbstractThe thymus represents the first lymphocytic organ to exhibit lymphopoietic activity in the fetal rabbit with lymphoblastic transformation beginning by 17 days of gestation, and lymphocytes appearing by 18 days, one to two days before vascularization. Lymphocytes are first evident in lymph nodes at 18 days of fetal development, in the spleen on the twenty‐third day, and in the appendix just prior to birth.Medium‐sized lymphocytes and rare blast‐like cells represent the first lymphocytic cells found in the lymph node anlage. Both of these cell forms appear simultaneously and are distributed randomly. Lymphocytes remain relatively sparse increasing gradually in number until several days prior to birth when their numbers increase rapidly. Coincident with the augmentation in lymphocyte population, lymphocytes tend to cluster near the vascular channels, and are present within the lumina and walls of the smaller veins in the node. Morphological gradations between mesenchymal cells and medium‐sized lymphocytes provide suggestive evidence that the initial population of lymphocytes within the node arise by the direct transformation of the stromal cells into medium‐sized lymphocytes. Less frequently, deeply basophilic blast‐like cells may provide an intermediate stage in lymphocyte differentiation. These cells differ from typical lymphoblasts because of their smaller size and irregular cellular contour.It is postulated that the initial population of lymphocytes formed in the lymph node anlage is derived from the transformation of mesenchymal cells and subsequent homoplastic lymphocyte proliferation and that during later fetal life this population of lymphocytes is complemented by the colonization and proliferation of blood‐born

ISSN:0002-9106    

DOI:10.1002/aja.1001240105

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1969

数据来源: WILEY

摘要:

AbstractGranulated juxtaglomerular cells have been identified in the media of afferent arterioles in the fresh water goldfish and in a marine English sole. Electron microscopy demonstrated the following five types of granules in the modified smooth muscle cells: (1) Small homogeneous granules near the Golgi apparatus; (2) larger homogeneous granules throughout the cytoplasm; (3) granules containing a bundle of hexagonally packed tubules; (4) autophagic vacuoles; and (5) granules containing membranous and granular debris. The granulated juxtaglomerular cells are morphologically similar to mammalian granulated cells and therefore may be the site of renin secretion. They exist with no relation to a distal tubule and hence appear to occupy an interesting position in the evolution of the juxtaglomerular apparatus.

ISSN:0002-9106    

DOI:10.1002/aja.1001240106

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1969

数据来源: WILEY

摘要:

AbstractImplantation inPedetes capensisis superficial and antimesometrial with the embryonic disc mesometrially oriented. As the blastocyst expands, the embryonic pole trophoblast proliferates and penetrates the epithelium at the mesometrial side to establish a massive trophospongial preplacenta. Maternal blood lacunae form in this, and a preplacental maternal circulation is soon established. Amniogenesis is by folding. A choriovitelline placenta develops on the preplacental surface. Yolk sac inversion is late. The bilaminar omphalopleure is permanent. Syntrophoblastic tongues penetrate the preplacenta and surround maternal spaces lined with an attenuated trophospongial cell layer, thus providing a hemodichorial barrier when the vascular allantoic mesoderm invades these tongues to form the lobular labyrinth. A typical countercurrent bloodflow occurs. A small allantoic diverticulum persists to term. Several fetal membrane characters, known to be evolutionarily “conservative,” are alike inPedetesand the more primitive sciuromorphs. These are the type of implantation, amniogenesis, yolk sac inversion, and allantois. The massive trophospongial preplacenta (Träger) suggests affinity with the Myomorpha and Hystricomorpha, but this is a highly variable character within the Rodentia. Therefore, it is concluded that on the basis of the fetal membranes the Pedetidae are somewhat specialized sciuromo

ISSN:0002-9106    

DOI:10.1002/aja.1001240107

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1969

数据来源: WILEY

摘要:

AbstractInitial cytodifferentiation of neuroblasts in the retina of chick embryos was investigated by means of silver impregnation, H3‐thymidine autoradiography, and electron microscopy. Utilization of various combined procedures with the same initial fixative demonstrated that the results of neurofibrillar staining are complementary, not contradictory, to information obtained from both autoradiography and electron microscopy.The question of a homogeneous versus a non‐homogeneous cell population within the neural epithelium was clarified by the closely related appearance of neurofibrils to the terminal mitotic cycle of some presumptive neuroblasts. Neurofibrils were observed in certain apolar pre‐division cells as well as in pairs of transitional apolar and bipolar daughter cells which apparently do not remain in the neural epithelium. At the ultrastructural level, aggregates of 60 Å neurofilaments were observed in configurations that corresponded to neurofibrillar networks. As the bipolar neuroblast moves into the ganglion cell layer, it would appear that much of the neurofibrillar substance is transported within the elongating peripheral process which becomes the optic nerve fiber. Further investigation of the relationship of neurofilaments to neurotubules in the neuroblast undergoing cytodifferentiation is now in pr

ISSN:0002-9106    

DOI:10.1002/aja.1001240108

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1969

数据来源: WILEY

ISSN:0002-9106    

DOI:10.1002/aja.1001240101

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1969

数据来源: WILEY