CHAP. 11.] FROM PORTSMOUTH TO TENERIFFE. 197 
S. virgula are in immense abundance and very generally dis- 
tributed (Fig. 26). Some of these species sometimes reach the 
coast of Britain, but an indraught of northern 
water which includes the British islands in a 
fork keeps out these oceanic things from our 
shores. If the British naturalist, to whom 
these things are usually unknown in a living 
state, will only push his towing-net work by 
a tug-steamer, or his own or a friend’s yacht, 
forty or fifty miles from the west coast of 
Scotland or Ireland, he will get beyond the 
arctic water, and will wonder, as I did only 
lately, at the new animal world in the shape 
of Pteropoda, Heteropoda, Siphonophora, and, 
above all, Polycystina and Acanthometrina, 4, 0 riptora col 
in all their wonderful varieties of form and ‘mela. Twice the nat- 
ural size. (No. 4.) 
sculpture, which will suddenly burst upon him. 
The Pteropoda extend far to the northward; one, Limacina 
helicina, with a delicate but very elegant spiral shell, and anoth- 
er, Clione borealis, which belongs to the shell-less subdivision, 
are frequently seen by arctic voyagers in such numbers that 
they actually color the surface of the sea in patches of many 
square miles in extent, and they are said to form a considerable 
item in the food of the Greenland whale, which strains them 
out of the water as it passes through his mouth, with his whale- 
bone sieve. I have dwelt on this little group because their his- 
tory is not very familiar, and because I hope to show that, small 
as they are, they play by no means an unimportant part in some 
of the recent geological processes of reconstruction. 
On the evening of the 17th of January, we passed Cape Tra- 
falgar of glorious memory, and sighted the light of Tarifa; and 
when we went on deck at sunrise the next morning, we were 
close under the Rock of Gibraltar, the endless line of batteries 
and the sulky iron-clads of the Channel fleet, which happened 
