he, 
SECTIONAL TRANSACTIONS. 
C. 373 
As the fossil remains of elephants and of man prior to the period of burial are 
found chiefly in interglacial gravels and sands, we have double means of subdividing 
Pleistocene time, namely, by calculations based on the glaciations and on the elephant 
remains found within the interglacial stages. The most abundant or outstanding 
species of fossil and recent elephants thus far found are as follows :— 
Maximum Enamel Lengths 
1. The Southern Mammoths, Archidiskodon . 3 ; . 8,000 mm. 
2. The Temperate 3 Parelephas F ‘ : . 10,000 mm. 
3. The Northern PP Mammonteus . : ; . 6,000 mm. 
4. The straight-tusked Elephants Palewoloxodon  . 2 . 6,000 mm. 
5. The African Elephants, Lowodonta . ‘ : , . 2,000 mm. 
6. The Indian oe Elephas ‘ ‘ : : . 7,000 mm. 
Dr. W. D. Lane. 
Palzontologists are generally agreed that during Geological time organisms have 
evolved from previously existing organisms by changes of character. They think 
so chiefly because their material falls into graded series. They use three criteria of 
relationship, namely (1) Morphic similarity, by which organisms exhibit graded 
series; (2) Order of succession in time, which shows graded series in chronological 
sequence—series which we call lineages on the assumption that the seriations are 
filiations ; and (3) Recapitulation, whereby an organism shows its ancestry in its 
ontogeny. Few are likely to dispute the principles implied in the first two criteria ; 
at most their adequacy to give proved lineages will be questioned: but periodically 
violent attacks, chiefly by embryologists, are made upon the principle of recapitula- 
tion. One has lately been launched with considerable force ; but it concentrates 
upon an exaggerated view of recapitulation, which few paleontologists have held, 
or are likely to hold, and admits much of what is left when these extreme views have 
been cleared away. While embryologists may admit recapitulation, palzontologists 
use it as a guiding principle. 
Assuming that our method is sound, and that our supposed lineages are real 
filiations, it is then seen (1) that a similar evolution is run through by many lineages 
both contemporaneously and successively, and (2) that individual characters run 
through a similar development in parallel lineages, and develop in the same lineage 
to a large extent independently of other characters ; so that, by differences in rate 
of development of single characters, individual terms in parallel lineages may present 
a very different appearance, although they may be at the same general stage of 
development. Thisis Orthogenesis, as now understood ; and however the environment, 
by Natural Selection or other means, may modify the course of development, this is 
the fundamental background on which it has to work ; just as, according to orthodox 
Darwinism, the environment, by means of Natural Selection, works upon indefinite 
individual variation. The origin of orthogenetic trends, on the one hand, and of 
individual variation on the other hand, is yet to be investigated. 
Prof. A. E. TRUEMAN. 
I. In the investigation of extensive series of invertebrate fossils the characters 
available for examination are fewer than in fossil Vertebrates, but the larger numbers 
of specimens make it possible to secure fuller information for statistical purposes. 
Hundreds of specimens of one ‘ species’ may frequently be obtained from a single 
layer, and it is suggested that, for all practical purposes, these may be regarded as 
constituting a ‘community.’ Investigations of such series appear to show that: 
1. The variability of certain fossils, such as corals and sedentary molluscs, is 
much wider than that of some ammonites and gastropods, but that the varia- 
tions are similar in character in both cases. 
2. Such communities as have been investigated appear to be homogeneous groups, 
the extreme types being relatively scarce and the intermediate types forming 
the main part of the community. 
3. Variation in one character appears to be relatively independent of that in 
another, from which it has been deduced that a ‘line’ of evolution consists 
of a plexus of anastomosing strands rather than a bundle of parallel strands. 
4, Most fossil species which have been investigated are therefore to be regarded 
as ‘impure’ species, to some e tent resembling those revealed by Mendelian 
analysis. 
