34 SCIENCE SKETCHES. 
starts and buries his head and neck in the now 
whirling sand, by a motion as quick as thought; 
his tail beats frantically about, and when again the 
clean sand lies smooth on the bottom, the little eyes 
are looking at you like two glistening beads, as if 
to witness your applause at so clever a trick. 
We have never seen Ammocrypta taste of food, 
nor do we ever expect to do so; for although its 
mouth bristles with teeth, its small size forbids an 
attack on any game which we can offer. Its qui- 
escent habits and the character of the bottoms to 
which it confines itself seem to indicate that its 
prey is minute if not microscopic. But speculation 
about what we do not know as to its food might 
lead us to speculation as to the origin of its char- 
acteristic features,— how, for instance, the hard 
snout, the transparent muscles, and the burrowing 
habits are consequent on its loss of scales, or how 
the loss of unnecessary scales and of pigment cells 
is consequent on its burrowing habits. Then, 
when we have finished these matters, we might 
inquire how it came about that there are “Johnny 
Darters” at all, and why no other continent has 
them. And we might go on with endless querics 
like these, which would take us far beyond the 
purpose of this article. We have wished only to 
introduce our aquarium friends, and to commend 
them to all lovers of beautiful things in Nature. 
