A common feature of hierarchical galaxy formation models is the process of “ inverse ” morphological transformation : a bulge dominated galaxy accretes a gas disk , dramatically reducing the system ’ s bulge-to-disk mass ratio .
During their formation , present-day galaxies may execute many such cycles across the Hubble diagram .

A good candidate for such a “ hermaphrodite ” galaxy is NGC 3108 : a dust-lane early-type galaxy which has a large amount of HI gas distributed in a large scale disk .
We present narrow band H \alpha and R-band imaging , and compare the results with the HI distribution from the literature .
The emission is in two components : a nuclear bar and an extended disk component which coincides with the HI distribution .
This suggests that a stellar disk is currently being formed out of the HI gas .
The spatial distributions of the H \alpha and HI emission and the HII regions are consistent with a barred spiral structure , extending some 20 kpc in radius .
We measure an extinction-corrected star formation rate of 0.42 M _ { \odot } \mbox { yr } ^ { -1 } .
The luminosity function of the HII regions is similar to other spiral galaxies , with a power law index of -2.1 , suggesting that the star formation mechanism is similar to other spiral galaxies .

We measured the current disk mass and find that it is too massive to have been formed by the current star formation rate over the last few Gyr .
It is likely that the star formation rate ( SFR ) in NGC 3108 was higher in the past .
With the current SFR , the disk in NGC 3108 will grow to be \sim 6.2 \times 10 ^ { 9 } { M } _ { \odot } in stellar mass within the next 5.5 Gyr .
While this is substantial , the disk will be insignificant compared with the large bulge mass : the final stellar mass disk-to-bulge ratio will be \sim 0.02 .
NGC 3108 will fail to transform into anything resembling a spiral without a boost in the SFR and additional supply of gas .