92 THE MARINE AQUARIUM. 
most bivalves, it should be borne in mind that they 
are apt to die off rapidly, and to cause a putrescence of a 
most obnoxious character, which soon spoils the water, 
and causes a general havoc. Another remark applicable to 
mollusks is this, that the Holids—members of the Nudi- 
branch, or naked mollusks—are destructive of anemones, 
and delight in nibbling holes in their coats, or eating off 
their tentacles ; whereas the pretty doris may be kept as 
long as it will live, in company with the most delicate 
creatures, without offering offence to any. The more 
varied the collection the more is our interest in its exa- 
mination increased ; and the possessor of a single vessel, 
or of a tank, and a few auxiliary jars, will be naturally 
anxious to preserve representatives of as many tribes as 
possible; and this may be done, to a certain extent, by 
appropriating the vessels to such creatures as agree ami- 
cably in confinement. It is, indeed, possible, if a vigilant 
watchfulness be observed, to bring together and preserve, 
for a length of time, specimens of creatures that are 
naturally antagonistic to each other; but where Crus- 
taceans can be kept apart in one vessel, with perhaps a 
few fish, such as gobies and blennies—a second appro- 
priated to anemones and madrepores—and a third to 
mollusks, madrepores, and tubeworms—there will be the 
greater certainty of success, and less supervision will be 
required. Crabs are very annoying to anemones, as they 
scratch and sprawl over the delicate creatures; and 
shrimps, prawns, and fishes frequently fall a prey to the 
barbed threads and the tentacles of the anemones; the 
latter also frequently take possession of the mouths of the 
