108 METHODS OF COLLECTING AND PRESERVING 
whole into spirit are almost useless for anatomical investigation. 
If they can be made to expand in a basin of sea-water, and are then 
plunged into a mixture of chromic acid and strong acetic acid, or 
into strong spirit or corrosive sublimate, the structure of the polyps 
is preserved. 
In preserving these forms, however, it is important to bear in 
mind that, if two or three slices about \ or ^ inch in thickness 
are preserved separately, they afford the most valuable material for 
investigation and study. Five per cent, formalin gives satisfactory 
results if the polyps can be induced to expand in a basin of sea-water 
after capture. 
Nearly all the Grorgonians have such a dense covering of spicules 
that preserving fluids cannot penetrate into their tissues. We are 
consequently almost entirely ignorant of the canal system of any 
but the most common species. 
When a Gorgonian is captured, therefore, in the dredge, a part of 
the " bark " should be stripped off and preserved separately in strong 
spirit, or allowed to remain attached to the axis, if the spirit in 
which the specimen is preserved can be kept of good strength, i.e. not 
less than 70 per cent. 
The Pennatulids can be fairly well preserved by immersion whole 
into spirit ; but it is always advisable, if more than one specimen 
of a species is obtained, to make a long incision into the axis with 
a knife before plunging into spirit, and any pinnae which can be 
snipped off with a pair of scissors and preserved separately yield 
good material for anatomical study. 
ECHINODERMA. 
Starfish may be prepared with the ambulacral feet in full dis- 
tension by allowing them to die in from 20 to 30 per cent, alcohol. 
Echinoids should be placed in a small quantity of water, and killed 
with chrom-acetic mixture No. 2, being removed from it as quickly 
as possible, as the acid corrodes the test. To preserve the internal 
parts, it is necessary to make two opposite openings in the test, so 
that the alcohol may penetrate the interior readily. 
