Observations on the Internal Structure of the Spermatozoid ofDictyota

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Abstract
The spermatozoid of Dictyota is shown to be structurally more like a vegetative zoospore than was the case in Fucus. The mitochondria, golgi, overall shape of the nucleus, nuclear membrane, fat bodies, and miscellaneous vesicles are as in a zoospore; there is, however, a vestigial chromatophore without an eyespot and the ciliary apparatus is specialized. In spite of the single flagellum there are two basal bodies inside the cell, one of which is apparently vestigial, ending blindy in the cytoplasm; both the a similar internal structure with nine fibres in the wall. A fibrous ‘root’, possibly homologous with the ‘proboscis’ of Fucus , arises near the outer side of the functional basal body; it is a band of about eight fibres passing through the cell without touching the nucleus but closely pressed to the inner faces of at least two mitochondria before ending in an unknown manner at the cell surface. The internal structure of the flagellum is normal but the fact that the median strand is marked by arow spines has been used to demonstrate is a conclusive way the facts of bilateral symmetry in the whole organ; Dictyota agrees exactly with Fucus and a previous error based on incomplete information has been corrected. The process of unwinding of the flagellum from the surface of the body after liberation from the antheridium is described and used to illustrate some unexpected properties of the surface membrane.

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