Myofibrillogenesis in vitro as seen with the scanning electron microscope

The present study describes an experimental approach whereby myofibrillogenesis and the three-dimensional arrangement of myofibrils present within cultured skeletal muscle cells can be examined using the scanning electron microscope. This procedure uses cells that have been cultured on gold-coated coverslips, and treated with Triton X-100 to extract the cell membrane and the soluble cytoplasm. Subsequent electroconductive staining by treatment with thiocarbohydrazide and osmium allows the myofibrils to be visualized. The images of myofibrils in various states of development observed by this method generally accords to those previously reported by transmission electron microscopy. Cell elongation and adhesion to the substrate causes mechanical stress from different directions which meet at branchings of the cultured myotubes. Many myofibrils are observed to run in the direction of the inferred stress lines.     

Blastoderm development in honey bee embryogenesis as seen in the scanning electron microscope

Summary

Based on observations in the scanning electron microscope, we describe the successive changes at the cell surface of fertilized honey bee eggs which, over a period of 20 h, lead to blastoderm formation. Each change starts in the differentiation center located in the anterior egg half and from there spreads as a wave towards both poles. However, one of the waves is heterogeneous: the protrusions or caps of oolemma which start enveloping the preblastoderm nuclei arise in different ways in the anterior third and in the more posterior regions of the egg cell. After the formation of these protrusions, three mitotic waves pass over the peripheral nuclei. The last of these blastemal mitoses results in a two-layered arrangement of peripheral nuclei, each surrounded by an outpocketing of the egg cell basally confluent with the central yolky part. This two-layered state after some time transforms into a single layer of columnar outpocketings which increase in height by extending their borders centripetally into the secondary periplasm (inner ‘Keimhautblastem’). The outpocketings disconnect from the central yolk mass as separate blastoderm cells only a short time before gastrulation. The events described here consume nearly 40% of the time period between oviposition and hatching; thus, and by comparison with most other insects, blastoderm formation in the honey bee is a very lengthy process.     

A morphological comparison of aortic elastin from five species as seen with the scanning electron microscope

The elastic laminae were extracted from thoracic aortas of adult animals including sheep, dogs, rabbits, cats and rats by treating them in hot alkaline solution (0.1 N NaOH at 75 degrees C) and observed with a scanning electron microscope. The elastic laminae are comprised of sheet-like internal elastic lamina, fibrous and membraneous elastin in tunica media, interlamellar fibers and hollow spaces which we presume were formerly filled with smooth muscle cells in the tunica media. These structures are the same in all five species except that the number of layers and the total thickness of the wall differs.     

The surface of the ovine omasum as seen with the scanning electron microscope (Mammalia,Bovidae)

The omasal surface with a range of horny papillae and stratum corneum has been examined using scanning electron microscopy. Other features of interest described include pits or holes in the surface of these corneal cells and hair-like structures associated with the lamina.     

Insect cuticular growth layers seen under the scanning electron microscope: A new display method

The scanning electron microscope (SEM) is demonstrated as a useful tool in the study of insect cuticular growth layers. The helicoids present in the endocuticle are shown to be comprised of discrete chitin fibrils, orientated in a staggered manner. Surface relief is used to explain the appearance of daily growth layer images under the SEM, the bulk of this work being performed on the short-horned grasshopper, Romalea microptera.     

Formation of the epicardium studied with the scanning electron microscope

The topographical characteristics of epicardial and myocardial cells of the embryonic chick heart are sufficiently distinct to enable reproducible identification by scanning electron microscopy. This made it possible to observe the development of the epicardial investment on the myocardial wall. The epicardial cells migrate from the mesothelium of the sinus venosus, cover first circularly the ventricular wall, and then extend cranially and caudally to ensheath the entire heart surface. Our observation argues against the generally accepted concept that the epicardium is a derivative of the outer myocardial layer. We strongly support the suggestion that the term “epimyocardium” is a misnomer [Manasek, F. J. (1969). J. Embryol. Exp. Morphol.22, 333–348].