404 Professor H. H. Swinnerton— 
If now the graphs of these measurements be examined (Fig. 9), 
it will be seen that the lines 3 to 8 follow one another in sequence 
and without crossing, so that the same conditions hold good for 
a phylogenetic as for an ontogenetic set of graphs. Again, the rate 
of change in one structural unit is not necessarily the same as for 
another, and thus the conception of the independence of the various 
serial changes receives further confirmation. 
It is interesting to observe that in 4 and 5, in which a reversal 
of direction of change takes place in some elements, the other 
elements come temporarily to a standstill. Again, in 6 and 7, whilst 
G and H progress rapidly, A and B remain stationary. These facts 
seem to indicate the existence of a principle of the conservation of 
evolutionary energy. 
Examete IV: Tue Gens CANINIA CYLINDRICA.! 
Another method of establishing lineages is resorted to when the 
material to hand is limited. It is based upon the quite reasonable 
assumption that a specialist on any group of fossils is thoroughly 
familiar with the various combinations of resemblances and 
differences of a wide range of types. This familiarity enables him 
to detect those forms which are so closely allied to one another that 
they must evidently belong to one genetic series, gens or lineage. 
Once he has established a reputation for reliability his conclusions 
are naturally accepted by his fellow-workers, until such a time as 
another specialist upon the same group arises to either refute or 
confirm his findings. The method of graphic representation explained 
above supplies an alternative means of testing the genetic affinity 
of apparently similar forms when the material is not abundant, and 
the investigator is not a specialist. 
In the late Dr. Vaughan’s paper on the Dinantian and Avonian 
he publishes a series of sections (pl. in, igs. 1-5) across five 
corals, which he calls mutations K, £, i, 1b 6 (cf. fig. 5 above), 
and which he regards as a gens or a series of “ continuously related ” 
forms. 
After making many different measurements of the elements in 
each of his five figures the following series of changes were found to 
be important and instructive :— 
(A) The number of minor septa. 
(B) The number of major septa. 
(C) The length of the major septa. 
(D) The distance of the outer ends of the septa from the epitheca. 
(E) The width of the dissepimental zone. 
These measurements are reproduced in graphic form in Fig. 10. 
From this it will be seen that the graphs K, £, 6, fulfil all the require- 
ments of a genetic series; that Z transgresses slightly across the 
other graphs, and presumably is not distantly removed from the 
1 Vaughan, Quart. Journ. Geol. Soc., vol. |xxi, 1915, p. 36 
