Figure 5
Early stage in the development of air sacs (AS) among parallel, double rows of book lung precursor cells anterior to the atrium. First instar, Centruroides gracilis. TEM. At this site somewhat inward from the atrium, the air sac channels begin with osmiophilic material (asterisks) that is apparently the result of merocrine secretion and/or enzyme action at the apical surface of the aligned cells. The basal surface of these cells is in contact with the primordial hemolymph channels (H), about 0.2 μm in width; one region (H') appears to be widening (~1.0 μm). Irregular wider regions like this gradually become more common. N, nucleus. Scale, 2 μm.