502 



PAUL E. LTNEBACK 



Fig. 15 



Fig. 19 



Figs. 15-19 Sketches showing the arrangement of the spiral and its apex. 

 Figure 15, the apical pattern, and figures 16 and 17, two methods of unwinding 

 the coil, from an embryo of 200 mm. Figure 18, the spiral and figure 19, its apex, 

 from an embryo of 180 mm. ; the spiral here presents half a revolution more than 

 that shown in figures 15 to 17. The letters mark points referred to in the text. 



