The morphological characteristics of the oviduct of 12 sexually mature rheas (Rhea americana) were studied. Only the left oviduct is developed as a long tube with a length of 122 +/- 23.1 cm, and is subdivided into infundibulum (15.2 +/- 4.0 cm), magnum (63.3 +/- 9.4 cm), isthmus (5.6 +/- 3.1 cm), uterus (16.0 +/- 4.2 cm) and vagina (11.5 +/- 1.4 cm). The mucous membrane of the oviduct, as a whole, possesses luminal folds covered by ciliated columnar epithelium with secretory cells. The infundibulum part presents a cranial opening with thin and long fimbriae with few tubular glands in caudal tubular portion. In the magnum, the largest portion of the oviduct, the folds are thicker and are filled with tubular glands. The isthmus is short and presents less bulky folds and a few tubular glands. A bag-shaped uterus in the cranial area shows thin folds, and in the caudal region (shell gland) more ramified folds with few tubular glands. The vagina has long luminal folds and a thick muscular tunic; no glands with sperm-storage characteristics have been observed. In conclusion, the oviduct in sexually mature rhea has morphological similarities with the other species of birds already described; however it presents its own characteristics to produce a big egg.

ABSTRACT.-Santos T.C., Sousa, J.A., Oliveira M.F., Santos J.M., Parizzi R. The rhea (Rhea americana americana) is a bird that belongs to the group of the Ratitas, order Rheiforme and family Rheidae. Macroscopic and microscopic morphology of the male genital organ (testes, epididymis, deferent ducts, and phallus) and the cloaca were analyzed in 23 emas, four chicken (2 weeks old), young (3 to 10 months old), and twelve adult ones (3 years old), from Cooperativa Emas do Brasil, RS and from CEMAS, Mossoró, RN. The testis of rhea had elongated shape and were located inside coelomatic cavity, in dorsal region of abdominal cavity, with medium length and width of 7.6±1.2cm and 2.6±0.7cm at adult animals; 4.5±1.5cm and 0.9±0.4cm at young animals; and 0.8±0.3cm, and 0.2±0.1cm at chicken. The testis were recovered by the tunica albuginea and its parenchyma had seminiferous tubules composed by spermatogenic epithelium and by sustentation cells, and also interstitial tissue, with interstitial endocrine cells, connective tissue and vessels. At the adult animals were observed all the cells from spermatogenic lineage, whilst at the youngs with 3 months the seminiferous tubules had a smale lumen with spermatogonia and undifferentiated sustentacular cells. The efferents ductus were composed by a cubic ciliated epithelium, while the epididimydis duct had a columnar epithelium. The epididymis was elongated and fusiform closely to medial testis board. The deferent duct had sinuous stretch at adult animals, rectilineae at young animal, convolute at its medium portion, decreasing its sigmoid shape at caudal portion, next to cloaca. The epithelium was pseudostratified ciliated, irregular lumen at adult animal, and circular at young animal, closely with urether. The cloaca was divided into three segments: coprodeum, urodeum and proctodeum. At urodeum the deferent ducts discharged into papillas at the ventral side wall, next to fibrous phallus's insertion. The phallus was a lymphatic fibrous organ, located at ventral wall, at the cloaca floor, and was composed by two portions: one rigid forked and twisted, and another simple spiraled and flexible, which normally was inverted. In forced exposition, the phallus had 14 cm in length. In a general way the Rhea genital organs shared the morphology from others birds, mainly those described to the ostrich.