The relation of germ cell degeneration to modifications of the testicular structure of Plethodontid salamanders

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Abstract
A study of the male sexual cycles of five species of Plethodontid salamanders indicated that annually occurring non‐functional regions at the anterior and posterior ends of the testis are associated with the two types of germ cell degeneration: (1) extensive degeneration of secondary spermatogonia in the anterior region; (2) complete degeneration in the posterior region, beginning with the young spermatocytes, of all germ cells except the primary spermatogonia. The improbability of the posterior degenerations being caused by a suggested climatic action is discussed. The presence only in urodeles of a caudo‐cephalic polarity of spermatogenesis over the length of the testis and of these degenerations seem more than a coincidence. The abortive spermatogenetic cycle of immature males shows a caudo‐cephalic sequence and the stages of degeneration that are identical with the adult. Inanition experiments indicate that the formation of secondary spermatogonia and the ability to form sperm are not synonomous. It is suggested, therefore, that normally more of the testis is activated than can be brought to a successful spermatogenesis. Since spermatogenesis moves caudo‐cephalically, the posterior end will be left outside the functional zone, and consequently the cells degenerate. The anterior degenerations and the failure of anterior end of the testis to be involved in spermatogenesis, mark the anterior regulation of the spermatogenetic process. Degenerations can be regarded as the by‐product of the regulation of overactivation.

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