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FEBRUARY 3, 192 3] 
hauled the cage in 1922, however, no urchins were 
found this time in the case, and no growth observed 
on the cage or shells. 
In 1921 Mr. Mathieson took a few sea-temperature 
observations which confirm the general indication 
‘that no higher sea-temperatures than 4° C. prevailed 
during the course and in 
the locality of the experi- 
ment. 
_ The almost complete ab- 
“sence of growth on July 16, 
_ 1921, on Mr. Huxley’s in- 
_ Spection is not significant, 
as I have found that failure 
_ to infect shells obviously 
with growth may occur 
in a similar period at 
ymouth. The absence 
of growth, other than the 
Sea-urchins, on August 24, 
‘1921, may or may not be 
due to slow rate of growth 
and cannot be discussed 
adequately here, but at Ply- 
mouth the writer has found 
that in a period of 3 to 6 
“weeks in summer experi- 
‘mental shells may become 
covered with extensive 
growths of marine organ- 
isms, some of which may in- 
deed have already attained 
‘sexual maturity. There is 
no doubt that the Spits- 
bergen sea-urchins were 
browsing on the oyster 
Shells in the cage. An 
analogous result has also 
n obtained in cage 
periments at Whitstable, 
where more than twenty 
relatively large starfishes 
(A. rubens), of a diameter 
‘of upwards to 16-8 cm. as measured from tip to tip 
of alternate arms, have been found on different occa- 
ons inside cages exactly similar to that used at 
tsbergen. In these cases there can be no doubt 
at the starfishes were attracted to the cage by the 
aad or dying animals inside the cage. 
The rate of growth of sea-urchins in temperate 
aters under natural conditions is not known with 
TiS aie 4q 
Fic. 2.—Showing ? rate of growth of a fixed population of marked cockles (Cardium edule) kept in a box with perforated 
The box was visited at intervals of one month, 
sides and top fixed to the bed of the River Yealm, near Plymouth. 
and the cockles measured. 
ber 10, 1919. 
Note the practical cessation of growth after about October 11. 
‘accuracy, but Elmhirst estimates (see NATURE, 
November 18, 1922)—and I agree—that E. esculentus 
_ (which is a large species) may grow to a diameter 
of 4 cm. in one year. In a similar cage experiment 
_ on oysters at Whitstable a sea-urchin, E. miliaris 
a relatively small species which does not attain 
NO. 2779, VOL. 111] 
NATURE 

A, size of cockles, August 16, 1919; B, September 12, 1919; C, October rr, 1919; D, November 10, 1919 ; 
————a 2 
2e2i- 22 23 24 260ge 
147 
more than about one-fourth the size of E. esculentus), 
was obtained on March 11, 1921, of a diameter of 
2-7 cm. (excluding spines) after the cage had been 
in the sea 65 days, giving a minimum growth in the 
period of t cm. in diameter. On another occasion 
specimens of E. miliaris, of a diameter of upwards 


Fic. 1.—Photo? of sea-urchins from the cage experiment at Spitsbergen, 1921, seen through a grating of the 
same mesh as the cage. (} natural size.) 
to 3 cm., were taken from the bottom of a floating 
coal-hulk, the London City, moored at Brixham, on 
August 1, 1911, after that vessel had been in the 
water after cleaning since April 1910. These sea- 
urchins were therefore rather more than one year old. 
The sea-urchins from the Spitsbergen cage experiment 
have not yet been definitely identified, but they 
probably grow to about the same size as E. miliaris. 
Other marine animals 
—for example, cockles— 
grow shell very rapidly 
in English waters in the 
warm months of the 
year, and may add from 
4 to6 mm. in length to 
: their shell per month for 
one. 6 or 7 months. (See 
a Sa. Fig. 2, which shows some 
unpublished results of 
experiments in 1919-20 
on growth in a fixed 
population of marked 
cockles kept in a per- 
forated box fixed to the 
bed of the River Yealm, 
near Plymouth.) 
Spitsbergen sea-urchins 

Thus the growth of the 
compares favourably in rate with that of calcareous 
marine animals in England, and indicates a rate of 
growth in marine animals generally in polar regions 
1 The writer is indebted to Mr. A. J. Smith for the photo (Fig. 1), and to 
Mr. E. Ford for the lettering in Fig. 2, 
