TEM micrographs of alligator nasal epithelia. A Low magnification of olfactory epithelium. Long slim supporting cells are filled with electron-lucent vesicles (vs). Note the area at the distal portion of the cell (asterisk) where vesicles are mostly absent. The surface of the supporting cells is covered with small microvilli. OSNs are rare (arrows). n – nucleus. B Higher magnification of the two different OSNs seen in A. One OSN (I) has few mitochondria. The cytoplasm is electron-lucent and contains microtubules. The other OSN (II) has abundant mitochondria and an electron-denser cytoplasm. Both cell types bear cilia and microvilli on their olfactory knobs. sc – supporting cell. C Apical ending of an OSN (type II) filled with mitochondria. The olfactory knob seems to bear only microvilli. However, serial sections reveal that cilia are present as seen in D. D The same type II OSN as in C showing microvilli and cilia.