Structure of microtubules: A study of freeze-etched and negatively stained microtubules from the ovaries of Notonecta

Summary Insect ovaries of the telotrophic type contain large numbers of microtubules within the tubes which connect an anterior trophic region to each oocyte within the ovariole. We have examined these microtubules using the freeze-etch technique and found that our observations correspond in many ways with the image of microtubules which have been subjected to chemical fixation. Obliquely fractured microtubules show sub-filaments within their walls, while both obliquely and longitudinally fractured microtubules display a periodicity of approximately 4 nm along many of the sub-filaments. In transverse fracture, a clear zone can be seen around individual microtubules and this confirms that the clear zones which are often seen around transverse sections of microtubules, are real features and not artefacts of fixation.The electron beam evaporation source equipment, used for shadowing the freeze-etched specimens, was obtained on a grant from the S.R.C. The AEI EM 802 electron microscope was purchased with M.R.C. Grant No. 971/55/B.