Abstract
Chick embryos of graded ages, ranging from freshly laid eggs to one week incubation, were prepared for electron microscopy.
Interstitial bodies are expressions of βground substanceβ that resemble structureless masses of cytoplasm without enclosing plasmalemma. They measure from 0.1 to ca. 1 ΞΌ in diameter. Toward the end of the first day of incubation they are found in the tissue space near to or in contact with the ectodermal boundary (basement) membrane. They seem to contribute to its increasing amorphous component. Microfibrils first appear close to or in contact with the ectodermal boundary membrane and are similarly related to interstitial bodies. At 44 hours interstitial bodies are especially numerous where the neural tube is separating from the ectoderm. Here boundary membranes have become intermittent and interstitial bodies appear to contribute to their repair. By the fourth day interstitial bodies are less numerous. Many appear to break up. Their edges tend to become dispersed into clouds of finely granular material, especially in areas of the tissue space occupied by wisps of microfibrils. The close association of amorphous ground substance and extracellular fibrils persists indefinitely.