Abstract
The description of the micro-anatomy of the motile cells of the brown alga Scytosiphon lomentarius include details of the structure and position in the cell of the following organs: plastid, eyespot, plastid diverticulum, nucleus, ciliary bases, mitochondria, fat bodies, cytoplasmic vesicles, microsomes and membranes, and a patch of canaliculated protoplasm possibly representing golgi material. Comparisons are made with the spermatozoid of Fucus and the zoospore of Vaucheria .