The surfactant system of the lung in the Mexican axolotl Ambystoma mexicanum

The broncho-alveolar space of axolotl contains numerous osmiophilic structures, which have been classified morphologically into 3 types of inclusions. Type I inclusions exhibited lattices of square to rectangular grid patterns with membranous elements 6 nm thick. This lattice was crossed by a 2 nm dense line. Type II inclusions were composed of 7 nm dark lines and 15.5 nm light lines in an alternating repeating pattern. Furthermore, the light lines showed an intrapenoid line of 2 nm. Type III inclusions consisted of concentric whorls of lamellae similar in form to spider webs. Only type III inclusions were identified in grand alveolar cells.