1897-98.] Prof. D’Arcy W. Thompson on Marine Faunas. 311 
On a supposed Resemblance between the Marine Faunas 
of the Arctic and Antarctic Regions. By D’Arcy 
Wentworth Thompson, C.B. 
(Read May 2, 1898.) 
The view that a peculiar likeness exists between the northern 
and southern extra-tropical faunas, add particularly between those 
of the Arctic and Antarctic regions, was suggested by Theel in 
discussing the remarkable deep-sea group of the Elasipoda , whose 
discovery we owe to the Challenger Expedition. A somewhat 
similar view is hinted at or referred to more than once in other 
Reports of the same Expedition. It was afterwards stated in an 
ampler way by Pfeffer ( Versuch iiber die Erdgeschiclitliclie Ent- 
ivichelung der jetzigen Verbreitungsverlialtnisse unserer Thierwelt , 
1891), and has of late been dealt with in great detail, and in 
relation to the antecedent causes that might have led to such a 
phenomenon, by Sir John Murray. On the other hand, Dr Ort- 
mann, considering the hypothesis from the point of view of our 
knowledge of the distribution of Crustacea, has rejected it entirely 
(“Uber Bipolaritat in derVerbreitung mariner Thiere,” Zool. JaJirh., 
1896; cf. also “Marine Organismen und ihre Existenzbeding- 
ungen,” ib ., 1897), and Dr Chun, dealing with the pelagic fauna 
(“Die Beziehungen zwischen dem arktischen und antarktischen 
Plankton,” Stuttgart, 1897), while showing how in truth a certain 
small number of forms are common to far northern and far southern 
seas, holds that the. facts are sufficiently accounted for by the con- 
tinuous distribution or gradual intermixture of forms in the depths 
of the intervening oceans under present conditions, without our 
needing to have recourse to an explanation of the phenomenon 
in the different conditions of a former age. 
The mere circumstance that so simple an issue should be open to 
question as the correspondence between the Arctic and Antarctic 
faunas on the whole, and the existence or non-existence of a large 
proportion of actually identical species in the two, is in itself clear 
