The play of the muscles and internal organs are plainly visible, and you can always tell what he has chosen for dinner. Diatoms and desmids form a portion of his diet. His mouth is below the wheel. When he is hungry he anchors himself by his forked tail and sets his wheel in rapid motion, which makes a powerful current sufficient to bring quite large objects to his head, frequently too large to admit into the mouth. He will often repeatedly try to take a desmid entirely too large for his mouth, and his manœuvres are quite comical as he whirls it round and round, nipping it on all sides. You will see by looking at the figure that everything has to be swallowed or taken within the body before it reaches the mouth. While the desmid is within the body the rotifer has control over it sufficient to take it into the mouth if it is of the right size, but if it is too large he soon becomes disgusted and ejects it with a sudden movement which sends it whirling rapidly away. And now he takes a smaller one and his jaws work vigorously a moment or two, when he swallows it almost entire, and we can plainly see the pretty markings and brilliant green color after it has passed into the stomach.
This large rotifer is plainly visible to the naked eye, and you will find it in both shallow and deep ponds, wherever water plants grow, during the months of July and August.
XI.—ON THE BEACH.
Many of our young people spend the month of August at the seaside, and if those who wish to learn something of the curious microscopic animals will stroll along the beach when the tide has receded, until they come to rocky places and little pools filled with salt water and various marine plants, they will find a form of animal life quite different from that in fresh water ponds. These little pools along the rocky coast are the homes of countless numbers of zoophytes—animals which have a stronger resemblance to plants and flowers than any we have found in fresh water.
Look for specimens for microscopic work on the surface of the rocks, on dead sea shells, and on the sea-weeds. On the sea-weeds you will often find a white filmy network which to the unassisted eye looks like simple white threads running and spreading in every direction, and at every angle of the network a tiny stem shoots up, branching out like a tree and making a miniature forest.
LAOMEDA.
Now if you apply a low power of the microscope, you will find the little forest is made up of a strange animal called Laomeda geniculata. (Fig. 1.) Each branch of this compound animal terminates and expands into a lovely vase and is the home of a polype. The polype is not a separate individual any more than the end of a growing branch is separate from the tree on which it grows.
When the creature is hungry he sends out from the margin of the vase from fifteen to twenty tentacles, ranged around the rim like the petals of a flower. Figure 1 shows one of these expanded polypes as seen through the microscope.