APRIL 29, 1915] 
NATURE 231 


cule above a critical velocity, ctherwise attachment is 
no longer possible. 
It was found that the positive ion remains un- 
changed in nature down to 1/20 mm., which was the 
lowest pressure tried. 
An account of. these experiments will appear shortly 
in the American Journal of Science. 
E. M. WELLISCH. 
Yale University, Sloane Laboratory, 
New Haven, Conn., April 6. 

Migrations in the Sea. 
Tue terms “anadromous” and *‘catadromous"’ are 
employed to distinguish fish which leave the sea to 
spawn in fresh water and fish which migrate from 
fresh water to the sea when they reach maturity. 
Gilson, in his paper, ** LjAnguille” (1908, Ann. d. 1. 
Soc. roy. Zool. et Malacol, d. Belgique, ¥. 43), proposed 
that the words should be used to define migrations to 
and from fresh water. The salmon, for example, is 
catadromous as a smolt, anadromous as a grilse, and 
so on. But unless new terms are to be created the 
words must be given a much wider significance than 
Gilson has suggested. The migrations of fish from 
the lower part of a river to the higher reaches, from 
a riyer to a stream, from the deep region of a lake 
to the shallows only differ in degree from _ the 
anadromous migration of the salmon. It cannot be 
said either that there is any difference requiring a new 
term in the migration of a fish from the sea into 
the lower part of a river or into an estuary. A fish 
which migrates from relatively deep water to the coast 
may also be said to have made an anadromous migra- 
tion. There are species which may spawn in fresh 
or brackish water, and species which may spawn in 
‘salt or in brackish water. In short, it may be said 
that fishes present every degree of anadromous migra- 
tion from mid-ocean to the upper limits of streams, 
and corresponding catadromous migrations. It is now 
proposed, therefore, that these words should be used 
to indicate the direction of the migration, however 
small or great that migration may be, whether passive 
or active, pelagic or demersal, seasonal or spawning. 
But even with the wide meaning here suggested the 
words cannot be applied to an important feature of 
migrations in the sea—migrations brought about by 
current. The Gulf Stream is utilised by fish and other 
organisms for the conveyance of eggs and larve and 
young to, or towards, the continent, and its branches 
are no less importantly taken advantage of to convey 
the products from the spawning ground to a region 
which may be at some considerable distance. The 
drift may often be said to be an anadromous one, but 
it is sometimes catadromous, and frequently could not 
be defined by either term. The migration of the 
mature fish is in contrast to the drift of the larva. 
This may be illustrated by reference to a species not 
a fish—the common edible crab. Cancer pagurus. The 
crabs on the east coast of Britain migrate, seasonally, 
catadromously from the coast for winter and anadro- 
mously to the shore region for summer. The mature 
females after ecdysis, sooner or later become ripe, and 
in response to the impulse thus conveyed migrate north- 
wards along the coast. During or after this migra- 
tion they ~become ‘‘berried.”” The larvae, when 
liberated, are planktonic, and are carried by the cur- 
rent to the south. If there were, as there is some 
degree of evidence to show that there are, particular 
regions which present large associations of berried 
females, the young crabs would reach the bottom most 
numerously in areas to the south, which may be said to 
be related to the regions where the larvz are liberated. 
Thus with regard to this species there is a migra- 
tion against the current of the mature females and a 
NO. 2374, VOL. 95] 
| 

migration with the current of the larva, and these 
migrations are clearly quite distinct from the seasonal 
movements which characterise the species at the other 
periods of life. 
The relationship of the spawning ground to the 
region where the demersal fry are deposited is better 
defined in the case of many of our species of flat fish 
and round fish, since it results in the formation of 
schools of seasonal migrants. 
To define these and other migrations which are inti- 
mately associated with currents it is necessary, there- 
fore, to introduce two terms which will serve to indi- 
cate movement against the current and with the 
current. My colleague, Prof. J. Wight Duff, recommends 
a Latin root, natare. The words suggested therefore 
are contranatant, swimming against the current, and 
denatant, swimming or drifting with the current. The 
words contranatation and denatation are also available 
to indicate the act or habit of migration against or 
with the current. A. MEEK. 
Marine Laboratory, Cullercoats, Northumberland. 

A Mistaken Butterfly. 
In this connection the case should be recalled of the 
Cleopatra butterfly of southern France and Italy, the 
close relative of our English Brimstone. By waving 
a grass-green butterfly net in its vicinity I have fre- 
quently attracted the yellow and orange coloured 
males, which will flutter after the net and endeavour 
to settle on it. The female is similarly coloured to 
the female Brimstone, but is rather larger. A blue net 

fails to attract them. H. BRYAN. 
REE MoCRAGRING 2 (OF VOLES AND VEILS 
COMMERCIAL USE. 
rue great consumption of petrol as a motor 
fuel, which last year, in spite of the dis- 
turbing element of war, rose to the enormous 
volume of 120 million gallons in England, and to 
nearly ten times that amount in America, has led 
to the attempt being made to add to the natural 
supply by the so-called “cracking” of the heavy 
residual oils left after the petrol and the lamp oil 
have been distilled off from the crude oil. 
The term “cracking” is one of those delightful 
Americanisms which express so exactly the mean- 
ing we wish to impart that it has been adopted 
universally—when a molecule is decomposed it is 
broken up: when it is merely resolved into simpler 
compounds it is “cracked.” The term first came 
over with carburetted water gas, when the oils 
fed into the carburetting chamber were said to be 
“cracked,” i.e., converted into hydrocarbon gases 
of high illuminating value, but not “broken ” into 
carbon and hydrogen. 
A less violent form of the same operation can 
be utilised to convert the heavy hydrocarbon 
molecules in oil of high specific gravity and boiling 
point into volatile liquids fitted for use as a sub- 
stitute for petrol. Most of the processes for 
doing this are based on a paper read by Sir 
Edward Thorpe and John Young before the Royal 
Society in 1871. This historical memoir was the 
first and only really scientific attempt to explain 
the actions that led to an increase in the yield 
of light hydrocarbons from a heavy oil under 
certain conditions of distillation, an action that 
