Larval, juvenile, and adult testes of Discoglossus pictus were examined to investigate how the extremely elongated sperm of this species, up to 2,500 μm, can be accommodated within the testicular tubules of the gonad. Seminiferous tubules in D. pictus are modest in number, of large diameter, and run straight from the posterior to the anterior ends of the testis. The modified testis structure originates in its unique development. The anterior part of the testis is composed of short and straight tubules forming the rete testis. The lumen of the seminiferous tubules is filled with bundles composed of sperm embedded in a periodic acid-Schiff stain (PAS)-positive matrix secreted by Sertoli cells. The formation of such extremely elongated spermatozoa is possible because of anatomical modifications including simplification of testis structure, enlargement of the diameter of testicular tubules, reduction in their number, assembly of rete testis tubules in the anterior part of the testis, reduction of the collecting system to a single duct, and the occurrence of sperm bundles embedded in secretion. Additionally, the secretion of a PAS-positive substance by Sertoli cells during spermatogenesis was described. Thus the urogenital system in D. pictus deviates dramatically from the typical structure of male gonads in other anurans.
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Vol. 47 • No. 2