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doi: 10.1002/aja.1001410303pmid: 4447074
The purpose of this study was to determine the developmental interrelationships existing between the lobes of the hypophysis and the prechordal mesoderm in the chick embryo.
doi: 10.1002/aja.1001410304pmid: 4614663
Between the 50th day of embryonic life Stage 20 (O'Rahilly and Boyden, '73; Wells and Boyden, '54). and the 30th week of gestation no reconstructions of the developing parenchyma of the human lung seem to have been attempted. To bridge this long gap, only two techniques have been utilized hitherto: counting the generations of branches in the growing segments of the lung and analyzing the changing cytology with the aid of the electron microscope. At least two important objectives remain: a knowledge of when the respiratory units known as pulmonary acini appear and the order in which capillary invasion of its component parts takes place.
doi: 10.1002/aja.1001410305pmid: 4447075
Bone resorption in newborn osteopetrotic rats and their normal littermates was measured in vivo and in vitro with different results. The resorption measured in vivo was that induced by injection of parathyroid extract after labeling bone matrix with 3H. Resorption was measured in vitro, by a commonly used method, as the release into the culture medium of 45Ca and 3H previously incorporated in vivo into bone mineral and matrix respectively. In osteopetrotic rats resorption induced by parathyroid extract in vivo was 34 percent less than in littermate controls, whereas the resorption measured in vitro was 26 percent greater in bone from osteopetrotic rats. In addition, the hypercalcemia induced by injections of parathyroid extract was only half as great in osteopetrotic rats as in normal littermates.
Kessel, R. G.; Beams, H. W.; Shih, C. Y.
doi: 10.1002/aja.1001410306pmid: 4548631
Cilia begin to grow from the free surface of some ectodermal cells during the neural plate stage (stage 13). Ciliary growth is not closely synchronized between cells in the same embryo, but the number of ciliated cells increases greatly during neural fold development and further growth in length of pre‐existing cilia occurs. Ciliated cells are numerous and widely distributed over the surface of early tailbud stages. However, cilia do not develop on cells in the neural plate and inner sides of the neural fold, and only an occasional ciliated cell is observed on the surface of the paired suckers. The number of ciliated epidermal cells per embryo increases during tail growth (stages 18–22). Ciliated epidermal cells persist after hatching (stage 20), but regression of cilia can be detected in stage 24 larvae. By late stage 25, most of the cilia have disappeared and the morphological variations observed indicate that the process involves resorption of cilia. Non‐ciliated (secretory) ectodermal cells from the neurula onward to stage 25 synthesize granules which are released to provide a mucous‐like coat for the embryo and larva. The surface structure of both ciliated and non‐ciliated ectodermal cells is described in sections studied with the transmission electron microscope and compared to the surface architecture of both cell types observed with the scanning electron microscope.
doi: 10.1002/aja.1001410307pmid: 4447076
The structural alterations of intralysosomal membranes were investigated in the rat lateral nasal and maxillary glands. In addition to conventional electron microscopical procedures, the following cytochemical reactions were applied: acid phosphatase, ruthenium red, phosphotungstic acid, and silver tetraphenylporphine sulfonate. Two forms of intralysosomal membranes were described, the myelin‐like figure and the aligned membranes. The former variety occurred most often in the lysosome and occasionally in some other organelles (e.g., secretory granule, multivesicular body, Golgi apparatus). Some figures were observed in the process of extrusion from the lysosome into the cellular interior. Furthermore, there were indications of the release by the cell of these membranes either into the lumen or toward the basal lamina. The acid phosphatase test revealed an association of the enzyme with the myelinated membrane in the lysosomal medium, in various cellular locations, and in the cellular environment. The possible importance of some interstitial cells in the transport of these membranes from the acinar base outward was noted. The other form, referred to as aligned membranes, occurred only as individual couples within the lysosomal interior. The formation of multilamellar complexes by further cross‐binding of membranous pairs was not observed. They displayed a focal occurrence of globules of apparently lipid material and a continuity with the already existing lipid droplets. Both types of altered membranes stained with phosphotungstic acid at pH 1.5, although they did not stain with silver tetraphenylporphine sulfonate. Most findings suggested that the two membranous varieties represented different patterns in membrane autodigestion.
Billings‐Gagliardi, Susan; De Webster, Henry F.; O'Connell, Maureen F.
doi: 10.1002/aja.1001410308pmid: 4447077
The migration of Schwann cells and their early association with axons were studied in transparent tadpole tail fins. Nomarksi optics revealed that in vivo these cells are pleomorphic, changing their shape by extending and withdrawing long, blunt pseudopods. Daily observations of the same fiber fascicles for a month or more combined with intensive short‐term studies of other tadpoles showed that migrating Schwann cells move sporadically at rates of up to 114 μm/day. They are usually, although not always, in contact with one or more axons. In the electron microscope, these migrating cells are similar in cytoplasmic structure to others that have settled down and begun to spread along axons; however, they possess no basal lamina. Later, Schwann cells become more spindle‐shaped and acquire a basal lamina. Schwann cell surface characteristics and the changes imposed by the presence of the basal lamina may be important in the establishment of permanent axon‐Schwann cell relationships. In our living material we were unable to visualize the intricate, rapidly changing associations between Schwann cells and small axonal fascicles that precede myelination. However, they are probably more complex than Speidel's studies would indicate.
doi: 10.1002/aja.1001410309pmid: 4447078
The development of the white and red pulp in spleen from thirteen human fetuses measuring from 72 mm to 145 mm in crown‐rump length (CRL) was studied using the electron microscope. This period follows the development of the primary vascular reticulum (Weiss, '73).
doi: 10.1002/aja.1001410310pmid: 4447079
Nineteen linear and three angular dimensions were measured for 590 left femurs derived from Bronze‐Age to present‐day population samples. Univariate analysis showed varying patterns of contrast between the populations, depending upon which femoral dimension was compared. Similarly, multivariate analysis also provided varying patterns of contrast between the populations, depending upon which group of dimensions was included in the analysis. Following standardization of the femoral linear dimensions against the maximum femoral length, in contrast, repeat multivariate analyses showed a progression from the Bronze‐Age to the present‐day samples, although there was only limited discrimination between the samples.
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