Figure 14

Formation of external cuticle in an outgrowth of hypodermal cells (Figure 4) from the base of the genital operculum after the third embryonic molt (stage 20). Limulus polyphemus. TEM. At this place in the cellular outgrowth, the cell membrane is somewhat pulled away from the inner surface of the external cuticle (Cu). Small electron-opaque particles (P1) can be seen in a row attached to the cell membrane while some particles (P2) are in the space between the cell membrane and inner cuticle surface. Other particles (P3) are attached to the inner cuticle surface. This sequence suggests that the particles are formed and released from the cell surface, and then the particles become part of the external cuticle layer. The particles differ in size from those in the cytoplasm of the adjacent cell so may be formed at the cell membrane by enzyme action on precursor particles within the cell. ER, endoplasmic reticulum. Scale, 1 μm.