The testicle performs two principal functions that make it the specific and primary organ of reproduction. The basic one is the formation of mature spermatozoa capable of fertilizing the egg: this is, of course, essential for the perpetuation of the race. The second function— the secretion of hormones—must be regarded as one supplementary to the formation of germ cells, since it contributes toward insuring delivery of mature spermatozoa in the proximity of mature eggs where fertilization can occur. Two concrete essentials are involved here: (1) the induction of behavioristic reactions, sometimes designated as sex drive or mating instincts, and (2) the provision of a vehicle of transportation for spermatozoa and of control of the ejaculate—either its discharge into the aquatic medium surrounding the egg in the case of lower vertebrates or its introduction into female passages by an organ of intromission. Just so far as either the formation of germ
MOORE CR. PHYSIOLOGY OF THE TESTIS. JAMA. 1941;116(15):1638–1644. doi:10.1001/jama.1941.62820150004009
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