1. The transformation of the spermatid into a spermatozoon takes place while the spermatid is closely associated with a Sertoli cell and it does not become free in the lumen of the seminiferous tubule until the spermatozoon is matured.2. In the early stages of transformation the cell goes through a growth period in which the entire cell gets larger and the chromatin material goes through an abortive preparation as if for division.3. During the period of elongation there is a reduction in the volume of the cell and a rearrangement of its parts.4. No "sloughing off" or loss of cytoplasm has been observed.5. The head of the spermatozoon is composed of two parts, the head proper which arises from the nucleus and the head cap or acrosome which arises from the idiosome and the idiosphere.6. There is a cytoplasmic bladder-like structure around the anterior part of the mid-piece.7. The tail is composed of three segments terminating in definite nodes.8. We find no indication of an unsheathed terminal filament eith...