From the Pennsylvanian subperiod of the Carboniferous period until well into the Permian, the most successful insects were primitive relatives of cockroaches. Six fast legs, four well-developed folding wings, fairly good eyes, long, well-developed antennae (olfactory), an omnivorous digestive system, a receptacle for storing sperm, a chitin-based exoskeleton that could support and protect, as well as a form of gizzard and efficient mouth parts, gave it formidable advantages over other herbivorous animals. About 90% of insects at the start of the Permian were cockroach-like insects ("Blattopterans").