stars can supply 4 to 37 $\times$ 10$^{\rm 48}$ photons s$^{\rm -1}$, indicating that all Group I shells can in principle be ionized by a single WR star. However, this is not proof that the only source of ionization is the WR star. Spectral classification of the brightest blue stars within the projected boundaries of the nebulae would be necessary to convincingly resolve this issue.

We now discuss which Group I shells may be physically associated with a solitary WR star. Our criteria are based on (a) the number of nearby massive stars (other than the WR star), and (b) a comparison of the sizes of the Group I shells with the sizes of WR nebulae in the LMC.

In Figure 4 we plot the sizes of Group I shells versus the number of nearby, potentially ionizing stars (including the WR star in all cases). Stars were selected if they were both (a) within one shell radius (and therefore within the boundary of the shell or shell fragment), and (b) have B - V colors $\leq$ 0 (photometry is taken from Magnier et al. (1992)). Only stars bluer than B0 (B - V = -0.3) can supply enough ionizing photons 