4.02 Professor H. H. Swinnerton— 
become stationary. In the absence of further evidence this 
may be neglected. 
As already seen in Example I, taken from Paleozoic echinoids, 
the rate of change of any one element is not necessarily the same as 
that of any other element. Had the rates of change been equal the 
lines would have been parallel. Comparing A and B, it will be seen 
that while A changes rapidly from 6 to d, B is stationary. When 
A has reached its maximum development and has become stationary, 
B progresses by leaps and bounds. The facts almost suggest a 
principle which may be described as the conservation of develop- 
mental energy. It is as though the energy were limited, so that when 
it is being used freely on one element, another must develop slowly 
or become stationary. 
100 8. 
904 3. 
80 ~~ / 
70 i 
vhs Re 
60 6. mare aS 
SJ. BN aan 
=0 4. OK Bases 
i NS a 
304 3. SS 
SON Pe 
~ 
a 
— 
oO 
ol Do 
0 7 
-j 0 ae eal 
-20- A 
: = 5 = Ba = ies 
Fic. 9.—Series of graphs representing the stages in the evolution of 
Zaphrentis delanouet. 
Exampte III: Tar Evonution oF ZAPHRENTIS DELANOUEI.! 
As already indicated, this is one of those rare cases in which the 
paleontologist’s dream of a perfectly worked out lineage is as near 
fulfilment as is humanly possible. That the series delanouet, parallela, 
constricta, and disjuncta, is a genetic series cannot be denied. The 
evidence adduced from the study of development, distribution, 
variation, and succession in the rocks is overwhelming. The measure- 
ments represented graphically in Fig. 9 were made upon the following 
figures on pl. xxxvii of Mr. Carruthers’ paper :— 
1 Carruthers, Quart. Journ. Geol. Soc., vol. Ixvi, 1910, p. 523. 
