The Refr,4ctory Period of Testis Rhythm in Birds,

A CCOKDINC; to Burger (1949: 222) the “problem of refractoriness is perhaps the greatest relatively unsolved problem in reproduction.” Actually, except in ultimate detail, the problem may have been solved (Marshall, 1949a; 1950a). The “refractory period” of Bissonnette (1931; 1937) and certain other authors is here defined as that period of the avian testis cycle when the tubules are in a state of post-spermatogenetic lipoidal metamorphosis and before the newly regenerated Leydig cells of the interstitium have become sufficiently lipoidal and mature to respond to neurohormonal influences ini& afed by natural factors in the environment. The term neurohormonal as used in this paper refers to the interaction of the exteroceptors, the hypothalamus, the anterior pituitary, and the gonads. The term lipoid has, of course, no precise chemical meaning, but used histochemically in its widest physical sense, it includes fats and all other animal substances that, in solubility, resemble fats (see Baker, 1946). It is hardly necessary to emphasize that the interstitial and tubule lipoids mentioned above have no direct connection with the gross deposits of peritoneal and subcutaneous fat that Wolfson (1942; 1945: 125) avers is a diagnostic concomitant of readiness to migrate. The period of testis reorganization described above varies in duration from species to species. While it is in progress the post-moult summer and autumn sexual display, described for many passerines and other birds, occurs.