In light microscopy, the human, ape, rabbit, cat, deer, and pig tissues revealed a pseudostratified, columnar epithelium with double layering in most areas, a basal cell layer, and a superficial columnar layer
(Figs. 1A 1B 1C 1D 1E 1F 1G 2C 2D 2E 2F 2G 2H) . The rat showed a multilayered epithelium
(Figs. 2A 2B) . The upper cell layers consisted of larger squamous elements over several layers of more or less cuboidal cells. Goblet cells were integrated in the epithelium of human, rat, and cat as solitary cells
(Figs. 1A 1B 2A 2B 2C 2D) and in the epithelium of human and rat as intraepithelial mucous glands
(Figs. 1A 1B 2A 2B) . The secretory product of these cells reacted strongly positive with alcian blue (pH 1.0;
Fig. 1H ). By contrast, the epithelium of ape, rabbit, deer, and pig contained no goblet cells
(Figs. 1C 1D 1E 1F 1G 2E 2F 2G 2H) . However, the epithelium of ape, rabbit, and pig contained many epithelial cells that showed mildly positive staining with alcian blue (pH 1.0) in the upper cytoplasm. The cell surface reacted strongly positive with alcian blue. The cells with the mild staining were mostly arranged in cell groups
(Figs. 1D 1F 1J 1K) . There were also epithelial areas without such cells or cell groups
(Fig. 1G) . Subepithelially, the lamina propria of the human lacrimal passage was composed of two strata: loose connective tissue containing elastic fibers and lymphatic cells and a rich venous plexus comparable to a cavernous body
(Figs. 1A 1B) . A surrounding cavernous system of blood vessels was also found in ape, rabbit, deer, and pig
(Figs. 1C 1E 2E 2G) , but was absent in rat and cat
(Figs. 2A 2C) . Small seromucous glands opening their excretory ducts into the lacrimal passage were integrated in the lamina propria of human and pig. In the pigs, seromucous glands were distributed along the whole nasolacrimal duct
(Fig. 2G) , whereas in the human specimens the glands were present only in the lacrimal sac in small numbers. None of the other animals possessed seromucous glands. The results are summarized in
Table 1 .