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Figure 10 | Frontiers in Zoology

Figure 10

From: The ultrastructure of book lung development in the bark scorpion Centruroides gracilis (Scorpiones: Buthidae)

Figure 10

Fusion and cuticularization of cell fragments in the primordial air sac. First instar, Centruroides gracilis. TEM. Here at the anterior end of an elongating air sac, cell fragments in the air sac lumen appear to be fusing together (F, F') to form a continuous tube. The periphery of the fragments has varying thickness of electron-opaque material, an indication that cuticularization and formation of the cuticle wall of the air sac is more advanced in some places (black asterisk). Dense particles (P) are present inside and at the periphery of the fragments as though aggregating from components inside the fragment. The thick osmiophilic material near the tip of the air sac (white asterisk) may result from aggregation of particles at the periphery of the fragment and/or secretion from the adjacent cells. At this stage, most of the aligned precursor cells (C) appear to be intact except for releasing cell fragments at their apical surface (apocrine secretion). The primordial hemolymph channel (H) is still narrow (~0.3 μm) at this site. Scale, 1 μm.

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