13 



Fig. 4 Diagram of the history of the race a, bearing the spine, for the entire twenty-two generations. 

 The anterior end and anterior individual are throughout to the right. The numbers at the left indicate 

 the generations, counting the original crooked specimen as the first. The arrows show the lines of 

 descent. Only the fission of the individual bearing the spine is followed out in each generation. For 

 details, see text. 



