Biermann (1979) has revived the earlier suggestion of Cameron and of Donn that the proto-cometary cloud and the proto-solar nebula were contiguous but distinct cloudlets, forming e.g. as fragments within the same massive interstellar cloud. As in Goldreich and Ward (1973) and Biermann and Michel (1978), the cometesimals are thought to have formed in a layer of dust that settled in the equator of a cloudlet maintained at a moderate density by a combination of thermal pressure and centrifugal force due to a high angular momentum. The solar nebula had much less angular momentum and so could contract to about the radius of Pluto's orbit before achieving centrifugo-gravitational balance. In this paper it is noted that modest variations in the initial parameters of fragments forming within the same massive magnetic cloud can yield both high and low angular momentum cloudlets (Mestel and Paris 1979). A fragment of mass M greater than a critical mass Mc, defined in terms of its magnetic flux F by GM2
c~F2/π2, contracts in approximate mechanical equilibrium, at the rate determined by the magnetic transport of angular momentum, and with centrifugal force remaining comparable with gravity. Rapid flux-loss at molecular cloud densities leaves a weakly magnetic, rapidly rotating, low-density cloudlet which could be the locale of cometary formation. If M<Mc, the magnetic stresses both limit contraction and enforce corotation with the surroundings. As flux leaks out slowly, the cloudlet contracts in approximate magneto-gravitational equilibrium, with centrifugal forces becoming a steadily smaller fraction of gravity. At the molecular cloud phase, rapid flux-loss leaves now a slowly rotating cloudlet, which can therefore become the proto-solar nebula. Whether a cloudlet is super- or sub-critical in mass will depend on the details of the fragmentation process in the parent cloud, in particular on the amount of mass agglomeration down the field-lines.