– 54 – Fig. 5.— The [3.6] -[24] vs [3.6]-[4.5] colors of Ophiuchus PMS stars with disks of different masses (left) and accretion rates (right). Transition disks (in the left side of the figure, with [3.6]-[4.5] < 0.25 ) tend to have much lower disk masses and accretion rates than non- transition objects. The disk masses of non-transition disk sample have been taken from Andrews & Williams (2007). The accretion rates of non-transition disks have been taken from Natta et al. (2006).