The neurosecretory system of the adult Calliphora erythrocephala : I. The fine structure of the corpus cardiacum with some observations on adjacent organs

Epoxy embedding methods of Glauert and Kushida have been modified so as to yield rapid, reproducible, and convenient embedding methods for electron microscopy. The sections are robust and tissue damage is less than with methacrylate embedding.

The aldehydes introduced in this paper and the more appropriate concentrations for their general use as fixatives are: 4 to 6.5 per cent glutaraldehyde, 4 per cent glyoxal, 12.5 per cent hydroxyadipaldehyde, 10 per cent crotonaldehyde, 5 per cent pyruvic aldehyde, 10 per cent acetaldehyde, and 5 per cent methacrolein. These were prepared as cacodylate- or phosphate-buffered solutions (0.1 to 0.2 M, pH 6.5 to 7.6) that, with the exception of glutaraldehyde, contained sucrose (0.22 to 0.55 M). After fixation of from 0.5 hour to 24 hours, the blocks were stored in cold (4°C) buffer (0.1 M) plus sucrose (0.22 M). This material was used for enzyme histochemistry, for electron microscopy (both with and without a second fixation with 1 or 2 per cent osmium tetroxide) after Epon embedding, and for the combination of the two techniques. After fixation in aldehyde, membranous differentiations of the cell were not apparent and the nuclear structure differed from that commonly observed with osmium tetroxide. A postfixation in osmium tetroxide, even after long periods of storage, developed an image that—notable in the case of glutaraldehyde—was largely indistinguishable from that of tissues fixed under optimal conditions with osmium tetroxide alone. Aliesterase, acetylcholinesterase, alkaline phosphatase, acid phosphatase, 5-nucleotidase, adenosine triphosphatase, and DPNH and TPNH diaphorase activities were demonstrable histochemically after most of the fixatives. Cytochrome oxidase, succinic dehydrogenase, and glucose-6-phosphatase were retained after hydroxyaldipaldehyde and, to a lesser extent, after glyoxal fixation. The final product of the activity of several of the above-mentioned enzymes was localized in relation to the fine structure. For this purpose the double fixation procedure was used, selecting in each case the appropriate aldehyde. Show more

In Hydra adjacent epithelial cells are bound firmly to each other by desmosomes of a type not described in detail hitherto. The most prominent feature of these desmosomes is the presence of a series of parallel lamellae which bridge the intercellular space and connect the two apposed cell surfaces directly. These structures, here termed intercellular attachment lamellae, display two peaks of density about 50 A apart. These dense lines appear in some instances to be continuous with the outer dense components of the plasma unit membranes of the attached cells. The presence of prominent lamellae in intercellular attachments is sufficiently distinctive to deserve special terminology; accordingly, the term septate desmosome is proposed. It is noted that septate desmosomes may have been seen in other animals in instances where published electron micrographs show cross-striations or prominent connections in regions of intercellular attachment. It is suggested that septate desmosomes in Hydra, in addition to binding cells firmly to each other, form barriers to the movement of water into intercellular spaces and thus help to protect the organism's internal environment. Observations on the use of phosphotungstic acid for improving contrast in materials embedded in epoxy resins are also recorded. Show more