400 Professor H. H. Swinnerton— 
arrangement in a coral showing maximum bilateral symmetry 
(Fig. 7, cs, ccs, a). As the symmetry changes the percentage number 
of radial septa increases until all are radial. Kven when major 
septa indicate only lingering traces of bilateral symmetry, the 
minor septa may still reveal it to a marked degree. These latter 
elements put in their first appearance on the counter-cardinal 
side of the section, and as their number increases they extend round 
to the cardinal side, until there are as many minor as there are major 
septa. The number of¢minor septa expressed as a percentage of — 
the total number of major septa thus becomes another measure of 
the serial change from bilateral to radial symmetry. 
Fic. 7.—Section of Zaphrentis delanowei (after Carruthers, Y.J.G.S., 1910, 
pl. xxxvii, fig. 8A). c.s. cardinal septum, c.c.s. counter-cardinal septum, 
athe shortest septum in one of the cardinal quadrants, 8 the shortest 
septum in one of the counter-cardinal quadrants. 
The following examples will serve to illustrate the way in which 
these numbers and percentages may be expressed graphically, and 
so be used for the solution of evolutionary problems. The measure- . 
ments used here have all been made upon the published figure of 
easily accessible and important pieces of work. The examples chosen 
are useful as tests for, as well as illustrations of, the method. The 
first is from a paper containing a careful and detailed description of 
the development of one coral. The second is from another, by the 
same author, in which the evolution of a species 1s traced in a manner 
closely approaching the ideal, and results are attained which cannot 
be refuted. The third is a fair example of the practice of linking 
together in series, mutations which, in the opinion of a specialist, 
“are continuously related either in space or time.” ! 
Examete I]: THe DEVELOPMENT OF CANINIA CORNUCOPIA. 
On plate vi of Carruthers’ paper ? on the development of Canina 
cornucopie, figs. 1b to 1y represent slices cut across the coral at 
different levels from the apex to the calyx. They, therefore, record 
the changes which are passed through in development. Many 
1 Vaughan, Quart. Journ. Geol. Soc., vol. Ixi, 1905, p. 183. 
2 Carruthers, GEOL. Maa., 1908, p. 158. 
