Dr. H.S. Bennett of the Anatomy Department, University of Washington, was used. Many sections 1/100 to 1/20 nu thickness were made with silver salmon spermatozoa for a continuation of an earlier study (5) In the earlier work it had been found that the tail was composed of an isodiametric filament containing eleven fibrils and was covered by a spirally wound, membranous sheath. Nine of the fibrils are of equal diameter, forming a ring in cross section, and are each made up of five protofibrils. remaining two fibrils are of smaller diameter, the middle of the ring of fibrils, The are located in and contain four proto- fibrils each. The new findings from sectioned material are as follows: The spermatozoan head is covered with two double membranes between which are many mitochondrial granules. Both the membranes and granules are sensitive to changes in osmotic pressure (Fig. 1). Both the proximal and distal centrioles are located well inside a pocket at the posterior end of the nuclear material. The more anterior proximal centriole is composed of globules in a ring configuration and is attached to the nuclear membrane. The distal centriole lies just posterior to the proximal centriole and is fused into the anterior