5.1. The I Systems (Plates I-V)
The very great majority of the I systems are probably of early spectral type. The small concentrations of light observed in particular in the first three illustrations are probably varieties of H II regions. The two systems illustrated in Plate V (NGC 4490 and 4214) are probably more complex than the others; it would be interesting to know if their linear dimensions and luminosities are greater than those of the systems illustrated in Plates I - IV.