The fine structure and morphological aspects of superficial and deep lymphatic vessels of Chiroptera' bladder (Vesperugo savi and Rinolophus f.e.) have been studied, under seasonal, physiological conditions of different lymphatic flux (winter lethargic state and summertime). The endothelial walls of subepithelial, intramuscular and subserosal-peritoneal, lymphatic networks show an uninterrupted course together with both simple and complex intercellular contacts, constantly jointed by specialized junctional complexes, such as zonulae adhaerentes and occludentes. The abluminal surface is often almost entirely encircled by a thick layer of fibrillary connective tissue. Seasonal cytological modifications of possible importance and morphological aspects typical of the each individual network have not been detected in the lymphatic endothelium. On the other hand the abundance distribution of clear intracytoplasmic vesicles and the frequent occurrence of micropinocytotic vesicles in the luminal and abluminal membrane surface have been shown. Canalicular structures have also been demonstrated, even if quantitatively less numerous with respect to those seen in the chiliferous vessels of the same species of Chiroptera. The Authors believe that most of the transendothelial transport in the above mentioned lymphatic vessels occur through the micropinocytotic vesicles and also through the intra-endothelial channels made up by the vessel wall, without any intervention of intercellular contacts or specialized junctions. The possible role of substances within the interstitium in inducing the appearance of canaliculi in the endothelial wall is discussed.