Abstract
The histological development of the paracloacal vascular body was observed in the male embryo of muscovy duck. On the 14th day of incubation, the primordium of the paracloacal vascular body was first recognized as an oval mass of mesenchymal cells containing a few blood capillaries and which lay lateral to the urodeum. The well-developed blood vascular system as well as the arterioles and venules was distinguished on the 16th day. The capillary cord and the peripheral lymphatic space partly appeared on the 18th day. After this stage the peripheral lymphatic space was gradually formed around the whole parenchyma of the body, and the internal lymphatic space, the trabecula and the capsule were also developed simultaneously. All of the main components of the paracloacal vascular body thus appeared by the 24th day of incubation. On the other hand, the lymphatic space of the fibrolymphatic body occurred from the peripheral lymphatic space of the paracloacal vascular body on the 19th day. Typical reticular lymphatic spaces were formed in the fibrolymphatic body on the 24th day.
