The acroblast of Helix spermatids is a duplex structure: it consists of an ‘externum’ (which appears dark by positive phase-contrast microscopy and becomes impregnated with osmium) enclosing a region called the ‘internum’.
Histochemical studies show the externum to be composed principally of phospholipid and to contain glycolipid, alkaline phosphatase, and an enzyme which splits thiamine pyrophosphate. The internum contains neutral mucopolysaccharide. Ribonucleic acid and acid phosphatase are not present in the acroblast.
These histochemical results suggest a homology between the invertebrate acroblast and the Golgi apparatus in vertebrate cells.
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