The Constitution says:
The Senate of the United States shall be composed of two Senators from each State, chosen by the Legislature thereof, for six Years. Immediately after they shall be assembled in Consequence of the first Election, they shall be divided as equally as may be into three Classes. [U.S. Constitution, Article I, section 3, clauses 1-2]
My question has two parts. First, how were the initial Senate classes selected? Logically, some would only be elected for two- or four-year terms, right?
Second, once the Senate classes were divided, how did the U.S. Senate maintain fairly even thirds as the country grew to 50 states? Presumably, the states were not all admitted in nice even intervals, and each state would want both Senators to start immediately so were there some Senators who took truncated terms?