Abstract
1. The spermatogonia contain twenty-six chromosomes, of approximately the same size and shape.2. There is a definite spireme stage with a simple plasmosome.3. The spireme segments into thirteen parts, of which twelve form rings, the thirteenth becoming attached as a chromatin mass to the plasmosome, which at this stage is double.4. In the growth period, when the twelve rings are definitely formed, the chromatin mass is bent in a crescentic band around the plasmosome, forming a chromosome nucleolus.5. This band represents a pair of idiochromosomes, and is bivalent like the rings, but always appears as a single body.6. First and second metaphases show thirteen chromosomes. Divisions are equal, so that the spermatids contain similar chromosome groups.
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