Dictyosome-like structures with cylindrical intersaccular connections (microtubules?) in guinea pig spermatocytes.

Structures superficially resembling dictyosomes were present in guinea pig primary spermatocytes and in spermatids in late stages of development. The dictyosome-like structures (DLS) were composed of 2 to 17 saccules. Each saccule averaged about 20 nm in thickness (membranes plus lumen) and 400 nm in diameter and was separated from adjacent saccules in a stack by an intersaccular space of about 12 nm. Single saccules separated from the DLS were also present. Tubules up to 60 nm in diameter were continuous with the edges of the saccules and sometimes extended for several micrometers into the cytoplasm. The membranes of the tubules appeared similar to the saccule membranes. Some DLS saccules and tubules had coated vesicles attached to them. A distinguished feature of DLS was the presence of microtubule-like structures, about 10 nm in diameter, that bridged the inter-saccular spaces. Some of these bridging structures appeared continuous through one or more saccules. The bridging structures were often arranged in linear arrays or in clusters of three to four. The membranes of the DLS appeared tripartite but stained differently from the membranes of the endoplasmic reticulum or Golgi apparatus. The inner (luminal) leaflet of the tripartite membrane usually appeared discontinuous or globular after fixation in glutaraldehyde-osmium tetroxide. The DLS could be distinguished from all other cellular components and may represent a new organelle unique to spermatogenesis.