372 
NATURE 
[JUNE 3, 1915 

effectively cooled out by repeated immersions than 
would be the case if a solid conductor of the same 
cross-sectional area were employed. 
The cases to which the process is applicable in 
scientific work are obvious and numerous, and it is 
needless to specify them. In view of the number of 
applications of a commercial and industrial value, as 
e.g. in the manufacture of incandescent electric lamps, 
mercury-vapour lamps, etc., the process has been pro- 
tected by patent in Great Britain and abroad; but I 
understand that this protection is not intended to 
restrict in any way its use in research laboratories 
or its application to any purposes of a purely scientific 
and unremunerative nature. F. F. S. Bryson. 
Natural Philosophy Institute, University of 
Glasgow, May 24. 

Eryonicus-Polycheles. 
In a recent publication on the Crustacea of Ireland, 
“Decapoda Reptantia of Ireland,’’ Part I., by C. M. 
Selbie (Fisheries, Ireland, Sci. Invest., 1914, I. 
(1914)), the question of whether the peculiar forms 
known as Eryonicus are larve of the crayfish-like 
deep-sea crustaceans Polycheles is answered to the 
effect that they are independent animals constituting 
a genus related to Polycheles. 
As these animals since the days of the Challenger 
Expedition have enjoyed a special interest as the 
modern survivors of a group almost until then be- 
lieved to be confined to Jurassic and Cretaceous times, 
I thought it might possibly interest some of your 
zoologist readers to learn about some of the results 
obtained through the study of the material collected 
in the North Atlantic by the Michael Sars in 1910 
during the cruise undertalken by the late Sir John 
Murray and Dr. Johan Hjort. 
To begin with, it must be mentioned that the best 
specific characters both in Polycheles and Eryonicus 
are derived from the arrangement of the spines on the 
carapace. Now a peculiar correspondence is observed 
in several species of the two ‘‘genera,’’ making it 
possible to ‘“‘pair’’ several of the Eryonicus species 
each with one of the Polycheles species, as will be 
seen from the following formula representing the 
position of spines in the median line of the carapace. 
In these formula, 1 and 2 denote single and double 
pointed spines, while 3 denotes a single blunt spine, 
arid c the position of the cervical groove, the rostral 
spines being to the left :— 
FE. faxont, Bouvier PMP BM aR he Ns 
~ . ro 
P. sculptus, Smith PEW IMG fR CAPS Fe J 
EF. coecus, Faxon ifs) eae eee alo eT \, 
P. sculptus pacificus, Faxon 2.1.2.1. €.2.2. 2 ff 
The two species a live in the Atlantic, the species b 
in the Pacific. The only difference between the two 
pairs consists in b having a spine on the cardiac area 
on each side, this spine being absent in all specimens 
of a examined by Mr. Selbie and myself :— 
E. hibernicus, Selbie... Dalale2eglsc- 222.302) ale 
P. nanus, Smith... Pie yar Oe (IS 
E. spinulosus, Faxon eho |f Mey oA) 
P. tanneri, Faxon Pw ign, G22 52 Re 
E. kempi, Selbie... bBo Moalinitozyguer ssw! | Vf 
P. typhlops, Heller ... ...  1.1.1.1.2.(2)e.(2).(2). 2° 
The figures within brackets in the formula for 
P. typhlops denote that these spines in some of Mr. 
Selbie’s specimens were of reduced size, single, or 
wholly rudimentary. It will be noted that the spines 
known or supposed to be blunt have no equivalent in 
the corresponding Polycheles. 
1 These spines are represented by Faxon as being pointed. I believe 
from analogy with all the Irish and AZichae/ Sars specimens that they are in 
fact blunt. 
NO. 2379, VOL. 95] 
Now, I ask, is it possible to explain the above corre- 
spondences as mere accident, or are they not to be 
taken as evidence of the Eryonicus species being in 
fact larval Polycheles ? 
One of the commonest objections to this theory is 
the giant size presented by some of the Eryonicus- 
specimens compared with the smaller Polycheles- 
individuals, though this need not signify much. Like 
so many other plankton animals, the Eryonicus are 
of a nearly jellyfish-like consistency, and it may as 
well be conceived that an Eryonicus can shrink into 
a small Polycheles, as that the Leptocephali, when 
turning into ‘‘montée,’’ lose about 78 per cent. in 
weight (in dry matter they lose over 32 per cent.), 
according to Dr. Johs. Schmidt, the Danish specialist 
on eels. 
If Eryonicus were adult animals, it would be rather 
remarkable that not a single egg-bearing female has 
been found among the fifty-nine specimens known to 
have been captured (Mr. Selbie, op. cit., mentions 
thirty-five specimens, and the Michael Sars got 
twenty-four). It cannot matter much that secondary 
male sexual characters in different stages of develop- 
ment have been found in a few of the largest 
specimens. 
Finally, it must be mentioned that one is at a loss 
where to seek the larvae of Polycheles, which do not 
seem to be very rare animals (the Irish research 
steamer Helga, for instance, obtained thirty-two 
specimens) if these larvae are not represented by 
Eryonicus. 
For literature and details of the species in question, 
see Mr. Selbie’s paper quoted above. 
Oscar SuND. 
Bureau of Fisheries, Bergen, Norway, May 8. 

The Age of the Earth. 
In Nature of May 6, Mr. C. E. Stromeyer states 
that two conclusions in my letter published in your 
issue of April 22 are not correct; he claims, first, 
that the amount of energy lost by the earth is not 
compensated by the heat received from the sun; 
secondly, that meteoric bombardment of the sun has 
been left out of account as a source of energy. 
As to the first point, the amount of energy lost in 
consequence of the temperature gradient in the earth’s 
cal 
cm."sec. 
times less than the total amount radiated, no useful 
purpose would be served by taking it into account. 
As regards the second point, any heat due tc 
meteoric bombardment up to date has been taken 
into account, as the sun’s mass as it is known to-day 
was inserted in the calculation. 
Perhaps the purport of my letter was not as clear 
as I could have wished. It was not so much my 
intention to weigh the evidence for or against an age 
of some twenty million years, as to emphasise the 
point that neither radio-activity nor any other known 
cause will account for a longer period. I have lately 
had the advantage of discussing the subject with Prof. 
Strutt, and must admit that the conclusions he has 
drawn from the helium contained in rocks appear 
unanswerabie. 
It would seem, therefore, that the origin of the 
sun’s heat cannot be referred to any known cause. 
Farnborough, May 15. F. A. LINDEMANN. 
crust is of the order 1°33 x 10-° As this is 6000 

Modern Substitutes for Butter. 
Tue issue of Nature dated April 8 contains an 
article relating to ‘‘Modern Substitutes for Butter,” 
which gives a highly interesting impression of the 
technical and scientific state to which the margarine 
| industry has developed in recent years. 

