It h a s lnceii demonstrated that low doses of ionizing radiations will produce chroniatid and cliromosome breaks which niay be followed by deletions, translocations o r other cliromosome reorganizations (see Sparrow, ?49 for a survey of chromosome studie?). IIigher doses are known to prolong meiotic and mitotic cycles, and will produce physical cliariges in the chromosomes which impede their movements (Marquardt, '38 ; Darlington, '42 ; and Koller, '43).
The clironiosoiiies of Triturus pyrrhogaster, the Japanese fire snlaniander, are among the largest known in the animal kingdom, some measuring SO0 in length (Durpee, in press). It was thewfore planned that the meiotic stages in spermatogenesis of this species should be subjected to x-radiations with arid without the maturation-stimnl~tin$ influences of the anterior pituitary hormone, to determine the rapidity with d i i c l i the physical changes in chromosomes are brought about by x-radiation. MATERIALS AND Ml3'I'HOl)S Triturus pyrrhogaster inales had been kept i n laboratorjaquaria f o r over one year, after receipt by air express from Japan.2 These salamanders were fed twice weekly with strips This document is hased on work performed under Contract AT-30-1-Gen 70, a These salamanders 13we kindly donated by Dr. W. R. Duryee of the Carnegie for thc Atomic Energy Commission.