The 9th Regt. was mustered into the service of the United States yesterday (Wednesday) afternoon by Maj. Wm. Austine, U. S. Mustering and Disbursing Officer for this State. The Regiment was reviewed in the morning by Gov. Holbrook and the colors presented by him in a brief and very appropriate speech, which was handsomely responded to by Col. Stannard in behalf of the Regiment, pledging their last drop of blood in defence of the flag and to maintain and restore the Constitution and Union.