Sarcocystis falcatula Stiles, 1893 is re-described. Intermediate hosts of the parasite which was earlier described as Sarcocystis debonei Vogelsang, 1929 are species of passeriform, psittaciform, and columbiform birds. In these birds, muscle zoites are 6.88 X 2.19 (4.8-8.4 X 1.2-3.6) micron and are enclosed in a cyst wall with regular protrusions, 1-5 micron long. The convoluted primary wall has multiple thin areas in the osmiophilic layer. Microtubules originate in the ground substance and extend to the tips of the protrusions. The only known definitive host is the opossum, Didelphis virginiana; rats, cats, a dog, and a ferret could not be infected from muscle cysts. Sporocysts from opossums infected from five different infected avian sources measure 11.2 X 7.4 (9.6-12.0 X 6.0-8.4) micron.

Coenogonium interplexum Nyl. is a green to yellow‐orange filamentous lichen commonly found on tree bark, rocks, and soil. The mycobiont is the ascomycetous fungus Coenogonium. The ultrastructure of the lichenized phycobiont, Trentepohlia, closely resembles that of the non‐lichenized form, a filamentous subaerial green alga. The mycobiont has a typical fungal ultrastructure, and the cell wall sometimes appears thinner at points of contact with the phycobiont wall. Several branched fungal hyphae are usually randomly arranged around a Trentepohlia filament, and may in some cases completely ensheath the alga. Although no haustoria were observed, this relationship may still be termed a lichen since there is some modification of the alga and the lichen is structurally distinct from the two symbionts.

The normal microscopic and submicroscopic structure of the lower respiratory tract of the budgerigar (Melopsittacus undulatus) is described and compared with other birds and mammals. Granular (type II) pneumocytes are confined to linings of air sacs, parabronchi, and their atria; however, their secretions (surfactant) cover the surfaces of the infundibula and respiratory space. Infundibula extend from the atria and give rise to the air capillaries, which branch and anastomose freely with those of adjacent infundibula and other parabronchi (interparabronchial septa are not found). Infundibula and the respiratory labyrinth are lined by a continuous epithelium of squamous pneumocytes, whose perikarya are concentrated in the infundibula and whose peripheral cytoplasm is markedly attenuated. The squamous pneumocytes of the respiratory labyrinth share a basal lamina with the blood capillaries that they envelop.

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