Classed IP addresses

Up to now I had not relizied how that they had divided the classes. Class A address have a zero for the first number of the octet (0-127) (01000000). Class B has a one as the first number of its octet (1000000)(128-191). Class C has a (10) as the first two numbers in first octet (11000000) (192-223). Class D (11100000) (224-239). Class E (11110000) (240-255). The chart on page 78 shows all the classes with clarity. But now I get how they defined them with how the octet numbers break over. For me the class divisions make sense on how they were derived.