THE ORIGIN AND DEVELOPMENT OF THE EARTH 123 
FIGURE 13. 
The spiral nebula M 74, in the constellation Piscium. This nebula 
contains a large central body and two well-defined and closely coiled 
arms. The arms bear a large series of knots that seem to be highly 
suited to serve as collecting centers for the nearby, scattered nebulous 
matter. Photographed at the Lick Observatory. From Chamberlin, 
University of Chicago Press. 
