Page:Popular Science Monthly Volume 31.djvu/766

746 family of the Terebratulæ, there are two smaller shells on the stone. The smallest species, of which three specimens lie on the middle of the stone, has the form of a heart, which is attached by its point. It shows a few dull-red spots on the middle of the shell, and is named Argiope. The other one, a little larger species, appears at the left in three specimens, with a straight hinge-border, and is broad and firm, and is called Megerlea.

We placed this piece of stone with its four species of shells, to which others that abound in the Mediterranean might be added, into a pail filled with sea-water, in which several other animals were stirring. We intended to watch the life-expressions of these fixed animals. Our patience was exposed to a hard trial. Hours passed away, without our being able to perceive the slightest movement. We had become tired and were yawning, when we thought we perceived the little Argiope mocking us. It was, in fact, gaping. The Megerlea, the snake-head terebratula, and the glass terebratula, followed its example and yawned too, but as discreetly as if they were in well-bred society. The valves parted from one another only a little; a few fine, glassy, glistening hairs, which could only be seen with the glass, appeared outside. That was all. Terebratulas have been kept for weeks and months living in glass vessels filled with sea-water, without any other movement being perceived than this gaping, which sometimes continued for hours. When they had gaped enough, they shut their shells, slowly and measuredly, as if they would sleep; and, when they had slept enough, they gaped again. Old noble by entail, which has grown fast to its estate, and sleeps or gaps its life away! But what do they feed upon? A closer investigation was required to find that out.

The two valves of the shell are not alike. The difference is greatest in the terebratula. One valve is wide, bellied, and runs into an upward-turned beak perforated by a round hole through which passes a short, round stem that is resolved outside of the shell into a bundle of thongs by which the animal fastens itself. The smaller valve rests as a cover upon this one.

We try to open the valves as they are opened in the gaping, but it is impossible to do it without force; so we have to break the shell open. Fig. 2 shows the opened snake-head terebratula magnified six times. The bellied valve is filled with two peculiar, half-moon-shaped processes, consisting of two bent, cartilaginous pipes, on the outer side of which stand a number of fringes which wind in a worm-fashion and circulate in constant movement. The space between these great arms, as they are called, includes two smaller arms, provided with similar fringes, which roll up helicoidally toward the bottom. Nearly all the space of the bellied shell is occupied by these forms; except that above, toward the point of the valve, may be seen some muscles, which open and shut the shell, and conceal from view the