544, TRANSACTIONS OF SECTION D. 
degenerate completely even in the larval state, and a number of other facts, point 
to their having passed through a condition similar to that of the parasitic Isopods, 
in which all the individuals are primarily males and subsequently females. 
2. Exhibition of Photographs of a Living Okapi. 
By Sir E. Ray Lanxester, A.C.B., FBS. 
3. The Pendulation Theory in relation to Geographical Distribution. 
By Professor H. Simrotu. 
According to the pendulation theory, the earth not only performs its move- 
ments of rotation and revolution in a day and a year respectively, but also has a 
much slower swinging movement (pendulation) about an axis which corresponds 
with the longest diameter of the globe, and has its poles in Sumatra and Ecuador. 
These may be called the ‘swing poles’ of the earth, or the east pole and the west 
pole respectively. In this movement the north pole and the south pole swing to 
and fro along a meridian which passes through Behring’s Strait and divides the Alps 
into an eastern and a western half corresponding nearly with the Valley of the 
Rhine: this may be called the ‘swing’ or ‘pendulation’ circle. The meridian 
passing through the east and west poles may be called the culmination circle, 
because each point of the earth in swinging towards the north reaches its most 
northerly position at the time when it crosses that circle. 
During the Glacial epoch Europe approached the north pole; during the 
Cretaceous and Eocene periods it was in a tropical or sub-tropical position, In the 
Palzozoic period also Europe was in a polar phase, which in the Permian period 
brought about a more ancient Glacial epoch. In Secondary times Europe moved 
in the direction of the equator. 
In consequence of the difference between the short and the long radii of the 
earth, Europe would emerge from the ocean when in the polar phase and be 
submerged under it during the equatorial phase, because the water, owing to the 
rotation of the earth, will always take the form of the geoid, whilst the hard 
crust will only take this form gradually and at a much later period. This explains 
the circular emergence and submergence of the solid land. 
This pendulating movement furnishes the key to the solution of a large number 
of problems in the geographical distribution of organic beings both in present and 
past times. As the earth was once much hotter than it is now, and the crust was 
in a molten condition, we must go back for the origin of living beings to an old 
intertropical stock in Cambrian or pre-Cambrian times. These beings made their 
way out of the tropics and into a cooler climate in a perfectly mechanical manner, 
the movement always reaching its maximum on the swing circle. In this migra- 
tion there were various possibilities. If the organism were capable of sustaining 
great variations of temperature (eurythermous), the northern boundary of its area 
would form a convex curve under the swing circle. If it were a stenothermous 
one, it would become extinct under this circle, and thus come to inhabit two 
separate areas symmetrically disposed with regard to the circle. If it were a 
plastic organism, it would become modified into a new variety or species. If the 
cooling were excessive, it would migrate into the water where the conditions of 
life are more uniform, The evolution of water animals might also take place in 
the opposite equatorial phase by mechanical submergence. The first of these 
methods has happened in the case of the Cetacea, the second in the higher marine 
Prosobranchs. The same process has taken place also in the more northern 
position, the organisms always moving sideways along the same parallel of 
latitude until they arrive at suitable conditions, 
The earth is divided by the culmination circle into two hemispheres, a Pacific 
and an Atlanto-Indic. In the former the water prevails; in the latter Europe 
and Africa occupy the position of the ‘ swing circle.’ The higher forms of animals 
and plants being those which inhabit the land, the Atlanto-Indic has taken the 
