THE ECHINODERMS OF THE WOODS HOLE REGION. 
549 
mollusk; but this whole subject has been so thoroughly investigated and reported by 
Mead (’99) that there is no reason to discuss it here. As food for fishes some of the 
echirioderms deserve mention, particularly Eehinarachnius parma and Ophiopholis 
aculeata , which, in spite of their most unprepossessing appearance from a gastronomic 
point of view, and their firm, calcareous skeletons, seem to be important items of 
food with the cod and some other fishes. The tile fish is known to feed very largely 
on a species of brittle star, Ampluura , its stomach often being completely distended 
with them. The smaller holotlmrians are also frequently eaten by fishes, though it is 
at least an open question how important an article of diet they may be. 
For the proper study of echinoderms, especially for purposes of identification, 
freshly killed material is the best. Alcohol is the best preservative, and should 
be used quite strong. Formalin is worthless, tending to make the tissues swell and 
become slimy, and dissolving the calcareous parts. All echinoderms are very sus- 
ceptible to Epsom salts (MgSO,), and it is probably the best available narcotic. In 
most cases it is not necessary to take any precautions, and the salt may be added to 
the sea water at once in considerable quantity. With some holotlmrians, however, 
more care is needed, and the salt should be added to the water a little at a time. 
Once thoroughly stupefied, echinoderms of all classes, except holotlmrians, can be 
killed nicely expanded by putting them into alcohol, 50 per cent or stronger. Some 
holotlmrians, especially Thyme briareus , are more difficult to kill satisfactorily, and 
hot water or acid - reagents serve the purpose better, as a rule. Of course, when it 
is desired to identify the specimen, acid reagents should carefully be avoided, for the 
calcareous parts of all echinoderms are essential to accurate identification, and espe- 
cially is this true of holotlmrians. Starfishes, brittle stars, and sea urchins are much 
more easily identified from well-dried specimens than from the best alcoholic ones, 
all important specific and most generic characters being based on calcareous parts. 
To prepare dry starfishes or brittle stars, they should be thoroughly narcotized, 
then placed in fresh water for a short time, then in strong alcohol for twenty-four 
hours, more or less, according to size, then dried as rapidly as convenient. The 
colors of many species are readily washed out in alcohol or even in fresh water, so 
that specimens prepared in the manner just described rarely retain a natural color. 
It is said the color may be preserved very satisfactorily by killing in 50 per centalcohol 
and drying rapidly by artificial heat. Sea urchins may be prepared in a similar 
manner, but care must be taken to see that the interior of the animal is thoroughly 
soaked in strong alcohol before drying. Most of the specific characters of all 
echinoderms, except holotlmrians, are easily seen with a hand lens, and usually with 
the unaided eye, even in young and small specimens. But for the proper identifica- 
tion of holotlmrians, a compound microscope is essential, as the minute particles of 
lime in the skin furnish the most important specific characters. To examine these 
all that is necessary is to cut out a small piece of the thin body wall, and after soak- 
ing it in water a few minutes, clear and mount in glycerin. If the body wall is 
thick, only the surface layer should be taken, and it should be treated with caustic 
potash (10 per cent or stronger) before being washed in water and cleared in 
glycerin. The same treatment is desirable when the body wall is heavily pigmented, 
or when the calcareous particles are extremely numerous and crowded into more than 
one layer. It is sometimes necessary to leave the piece of skin in caustic potash for 
several days, especially if the specimen has been in alcohol for some time. 
