They all, also, have a heavily sclerotized head case called the head capsule. They have one pair of antennae. 3 and gonopods on seg.
Segments fuse during dvt.
As we have seen in other groups of arthropods, a well-developed tracheal system is associated with high levels of activity in these animals even in the face of a relatively inefficient open circulatory system. Rectum reabsorbs water from wastes and uric acid is the primary excretory product. Y-organ produces molt promoting hormone. Lots of insects do this at one stage or another in their development.