TRANSACTIONS OF SECTION C. 773 
him be very full, distinguish the differences between fossils which are variations 
from a contemporaneous dominant form, such as ‘sports,’ and those which have 
been termed ‘ mutations,’ which existed at a later period than the forms which 
they resemble. The value of the latter to those who are attempting to work out 
phylogenies is obvious, and their nature can only be determined as the result of 
very laborious and accurate field-work ; but such labour in such a cause is well 
worth performing. The student of phylogeny has had sufficient warning of the 
dangers which beset his path from an inspection of the various phylogenetic trees, 
constructed mainly after study of existing beings only, so 
‘, . . like the borealis race, 
That flit ere you can point their place ;’ 
but recent researches amongst various groups of fossil organisms have further 
illustrated the danger of theorising upon insufficient data, especially suggestive 
being the discovery of closely similar forms which were formerly considered to be 
much more nearly related than now proves to be the case; thus Dr. Mojsisovics! 
has shown that Ammonites once referred to the same species are specifically dis- 
tinct, though their hard parts have acquired similar structures, sometimes con- 
temporaneously, sometimes at different times, and Mr. S. S. Buckman? has observed 
the same thing, which he speaks of as ‘heterogenetic homceomorphy’ in the case 
of certain brachiopods, whilst Prof. H. A. Nicholson and I* have given reasons for 
supposing that such heterogenetic homceomorphy, in the ease of the graptolites, 
has sometimes caused the inclusion in one genus of forms which have arisen from 
two distinct genera. As the result of careful work, dangers of the nature here 
Suggested will be avoided, and our chances of indicating lines of descent correctly 
will be much increased. It must be remembered that, however plausible the lines 
of descent indicated by students of recent forms may be, the actual links in the 
chains can only be discovered by examination of the rocks; and it is greatly to be 
desired that more of our geologists who have had a thorough training in the field 
should receive in addition one as thorough in the zoological laboratory. Shall I 
be forgiven if I venture on the opinion that a certain suspicion which some of my 
zoological fellow countrymen have of geological methods is due to their compara- 
tive ignorance of paleontology, and that it is as important for them to obtain 
some knowledge of the principles of geology as it is for the stratigraphical 
paleontologist to study the soft parts of creatures whose relatives he finds in the 
stratified rocks ? 
The main lines along which the organisms of some of the larger groups have 
been developed have already been indicated by several paleontologists, and 
detailed work has been carried out in several cases. As examples, let me allude 
to the trilobites, of which a satisfactory natural classification was outlined by the 
great Barrande in those volumes of his monumental work which deal with the 
fossils of this order, whilst further indication of their natural inter-relationships 
has been furnished by Messrs. C. D, Walcott, G. F, Matthew, and others; to the 
graptolites, whose relationships have been largely worked out by Professor C. 
Lapworth, facile princeps amongst students of the Graptolitoidea, to whom we 
look for a full account of the phylogeny of the group; to the brachiopods, which 
have been so ably treated by Dr. C. EK. Beecher,* largely from a study of recent 
forms, but also after careful study of those preserved in the fossil state ; and to the 
echinids and lamellibranchs, whose history is being extensively elucidated by 
Dr. R, T. Jackson * by methods somewhat similar to those pursued by Dr. Beecher. 
1 E. Mojsisovics, Abhandl. der hk. k. geol. Reichsanst., vol. vi. 1893. 
? §. 8. Buckman, Quart. Journ. Geol. Soc., vol. li. 1895, p. 456. 
*° H. A, Nicholson and J. E. Marr, Geol. Mag., Dec. 4, vol. ii, 1895, p. 531. 
- 4C, E. Beecher, ‘Development of the Brachiopoda,’ Amer. Journ. Sci., ser. iii. 
vol. xli. 1891, p. 343, and vol. xliv. 1892, p. 133. 
5 R. T. Jackson, ‘ Phylogeny of the Pelecypoda,’ Mem. Boston Soc. Nat: Hiist., 
vol. iv. 1890, p. 277; and ‘Studies of Palvechinoidea,’ Bull. Geol. Soc. Amer., 
vol, vii. 1896, p. 171. 
