A MODIFICATION OF THE URODELE TESTIS RESULTING FROM GERM-CELL DEGENERATION

Abstract

1. The testes of several species of Urodeles frequently possess a slender caudal extension or appendage suggestive of a functional reduction of the organ.2. This caudal appendage is present only during the summer months. It disappears in autumn, to reappear in the following spring.3. Study of its cyclic changes indicates that its appearance is due to degeneration of the germ cells of the more caudal lobules of the testis.4. The germ-cell degeneration is interpreted as resulting from the unfavorable conditions of winter; the cells most advanced in development are apparently the most susceptible and they alone degenerate.5. The caudo-cephalic order of development of the germ cells results in the localization of the most advanced stages in the caudal end of the testis; their degeneration reduces this region to a slender caudal appendage.6. The development of spermatogonia for the next spermatogenetic cycle occurs at the normal time in the appendage, increasing its size to that of the "body" of the testis; this explains the annual disappearance of the appendage in species possessing it.7. The development of an appendage of the type here described is possible only in certain Urodeles with a testis of simple type and marked polarity. It is of almost constant occurrence in Gyrinophilus and Plethodon glutinosus.1Postscript.—Since the foregoing paper was placed in the hands of the editor, a number of Urodele males captured in the spring and summer of 1924 have been examined. These animals, particularly in the case of one species, show a very striking difference from those of the four preceding years. While among twenty-two adult Plethodon glutinosus males captured between January and September in 1920, '21, '22, and '23, only one lacks the characteristic appendage above described, not one of the nine taken in 1924 possesses this structure. In those males captured earliest in the season (May and early June, 1924), normal spermatocytes still occupy that caudal portion of the testis in which spermatids are commonly found to have been formed in early autumn. Evidently few or no maturation divisions occurred in the fall of 1923, and as a result, few or no spermatids were present to degenerate during the winter of 1923-24. Absence of the appendage in 1924 is the natural result of such retarded spermatogenesis.The failure of the maturation divisions to begin in the fall of 1923 is undoubtedly a consequence of climatic conditions obtaining during the spring and possibly also the fall of that year. Weather bureau records at Ithaca show that the average temperature for May, 1923, was 4.8 degrees below that of the normal (average of 30 years). Plethodon males taken in July, 1923, show spermatogenesis retarded by from two to four weeks as compared with males taken in other years,—a retardation presumably due to the lowered temperature above noted. This retardation apparent in July would undoubtedly delay completion of the current spermatogenetic cycle and postpone the beginning of the cycle following. At any rate, no maturation divisions occurred in the fall of 1923 in this species. The spermatocytes present in the testis were either delayed in their early development, or their maturation divisions were later prevented by lowered October temperature. Both factors might conceivably be involved in effecting the end result, the elimination of the usual autumnal maturation. Since only spermatids undergo degeneration during winter in Plethodon glutinosus, no appendage appeared in the following season.Of the other Urodele species developing an appendage, Plethodon cinerius shows an effect comparable to that in Plethodon glutinosus. In Eurycea the appendage was found during 1924 much as in preceding years. No Gyrinophilus males were examined.The complete absence of the appendage here reported strikingly supports the writer's statement that it is a structure due to environmental effects upon spermatogenetic processes, and as such, may vary from year to year even in the same male.