Complex sentence: The instrument which corresponds to the violin in the violin octet is the mezzo violin, tuned the same as a violin but slightly longer; the strings of the mezzo violin are however of the same length as those of the standard violin.
Split into simpler sentences: The instrument which corresponds to the violin in the violin octet is the mezzo violin, tuned the same as a violin but slightly longer. The strings of the mezzo violin are the same length as those of the standard violin.