Figure 7
Cell fragmentation as an early stage in the development of air sacs (AS) among double rows of book lung precursor cells. No widening of the air sac entrance is evident at the origin of the air sacs in the cuticular wall (Cu) of the atrium (At), but two streams of elongate cell fragments separate a double row of cells from adjacent rows. The cells contain many small particles (P), possibly ribosomes and/or granules. The latter may contribute to the formation of air sac cuticle in later stages (e.g., Figs. 12, 13). N, nucleus. Scale, 2 μm.