TRANSACTIONS OF SECTION D. 545 
greatest share in the evolution of living beings. The perfection of this process, 
however, depends upon the alternation of emergence and submergence. The out- 
lines of Africa are too uniform for this process to be very effective, the irregular 
coast-line of Europe producing more striking effects in this direction. Therefore 
Europe (including Africa north of the Sahara) has always been the centre of 
organic evolution. All organisms have been dispersed hence in the manner 
just described, They have migrated eastwards and westwards or south-westwards 
to the west pole, or even further, till they arrived at a suitable environment. 
Those groups which are not now confined to a single locality inhabit places which 
are symmetrical with respect to the ‘swing circle,’ or points which have a similar 
relation to the swing poles, e.g., California and Japan, Chili and New Zealand or 
East Australia, Spain and South Russia, &c. In many cases the mode of dis- 
persal is proved by the organism still inhabiting intermediate stations, or its 
remains being found there ina fossil condition. Numerous instances of this might 
be mentioned, the human race furnishing one of them. 
Not only is the geographical distribution of creatures now living explained by 
the pendulation theory, but also the geological periods themselves. A geolo- 
gical period is not a definite epoch extending at the same time all over the earth, 
but it is a wave originating in Europe and spreading over the globe along the 
lines indicated above. 
If the great epochs correspond with the great pendulation movements, then the 
shorter periods (e.g., the interglacial periods) are to be explained by its being 
complicated with other movements. The north pole of the earth moves round in 
a circle in a period of about twenty-six thousand years; hence the pendulation 
cannot proceed in direct lines, but must have a screw-like form, the straight line 
along the ‘swing circle’ being the result. The smaller alternating secondary 
movements give rise to the shorter periods. 
The elevation of the mountains is the consequence of their passing into a 
polar phase. The land rises more and more above sea-level as it approaches the 
north pole, but eventually it also succumbs to the centrifugal force of the earth’s 
rotation, breaks down, and becomes faulted. The greatest development of this 
process takes place in the latitude of 45°; the lines of elevation are those along 
which the organisms spread, and they also mark out the places in which earth- 
quakes occur. 
The continent of Africa would seem to be the primary cause of this pendula- 
tion. Without Africa the new world and the old world would present a some- 
what symmetrical appearance, and the process of pendulation is gradually bringing 
this to perfection, It has almost succeeded in the Pacific hemisphere, but in the 
Atlanto-Indic hemisphere the continent of Africa forms an obstacle which cannot 
be removed by denudation or other causes. Africa seems to be an old moon 
which has fallen upon the earth in a direction from the south-west. 
4. On the Systematic Position of Polypterus. By E. 8. Goopricn, F.R.S. 
Polypterus and Calamoichthys, from the rivers of tropical Africa, are two 
closely allied genera which together form the order Polypterini. 
That they are forms of very exceptional interest, that they occupy a very 
isolated position in the classification of fish, there can be no doubt. They are 
distinguished from all living fish by many important anatomical characters and 
have uo close living relatives. One need only mention the presence of rhomboid 
ganoid scales, of paired gular plates, of a persistent spiracular gill-slit, of true 
clavicles, of a ventral bilobed air-bladder, and a straight tail, forming a combination 
unknown in any other order. 
Owing to their lobate pectoral fins, paired gulars, rhomboid scales, and out- 
wardly diphycercal tail, and to a considerable resemblance in the disposition of 
the roofing cranial bones, Huxley placed the Polypterini in the group Crosso- 
pterygtt in his famous paper on the Classification of Devonian Fishes! Polypterus 
' «The Systematic Arrangement of the Fishes of the Devonian Epoch,’ Wem. Geol. 
Surv., 1861. 
1907, NN 
