INSECTS AND HIGHER ANIMALS

We have glimpsed some of the great diversity in the worlds beneath the waves, and it is hoped that they will be often revisited. We have seen how thoroughly dependent these animal types, as well as lower plants, are upon being directly in the waters that bathe them almost constantly. But from these early beginnings, animals have found ways of freeing themselves from direct immersion in water, just as plants, over vast periods of time, have raised themselves out of it, to the heights of the mighty oak or sequoia, to the cactus in its parched environment, and to the perfection of such seed-bearing flowers as the lily and orchid. There are a huge number of kinds of specialized cells to be found as animal forms become more complex.

Many types of animal cells are more difficult to obtain than plant cells look closely if you have microscope, and in many cases, ordinary microscopic inspection is not sufficient to reveal cells well. Most must be prepared, sectioned into exceedingly thin slices and stained a skilled and often complicated procedure. Such microscope slides can be purchased, however, and a catalogue from biological supply houses will list them. Science and biology teachers will be able to give assistance here.

But there are still many specimens you yourself can derive great satisfaction from examining in the microscope. Your interest will be greatly increased if you keep a notebook or system of index cards containing data, diagrams and descriptions, look up information to explain better what you see and consider what you see with a questioning approach. Why is a feather made that way, how does it work, and what are those things coming off the other things called, what is the relation of feathers to coverings of other animals? If one book does not tell you what you would like to know, go on to another or do so anyway. Whatever is suggested here is merely a starter.
The Animal Parade

In science and biology only a small bit of animal tissue is necessary for examination. Here are some kinds of tissues which need little or no staining, although you may profitably experiment with various kinds, such as iodine, methylene blue, eosin, haemotoxylin, neutral red or gentian violet. Animal muscle red meat beef, pork, and more fish or fowl muscle meat fat from beef, pork, chicken, and more tendon from a beef joint cartilage or gristle from a chicken Joint fish scales of all kinds skin from canned salmon skin from frog shed snake skin muscle from fish intestine or animal heart.

Muscle cells are unusually large and long and can be quite well distinguished at 100X magnification. Tease loose with teasing needles some of the cells, called fibers, as gently as possible. Look for the all-important cross lines or striations, a characteristic of all voluntary muscles. Such muscles are somewhat different from involuntary muscle, or that which cannot be directly controlled, as is found in the stomach and intestine. There are many nuclei in each muscle cell, which may show up better with neutral red or other stain you may even try red ink.

A speck of fat can be squashed down with a slide cover, and the large, globular cells clearly revealed. You may also find layers of it between muscle fibers. Cartilage, or gristle, is very different from both fat and muscle, a good piece may be obtained from, for example, a joint in a chicken wing. If a good, even section is difficult to make, examine around the thin edge of the section you cut. Bone itself cannot be prepared without special equipment although a hand lens is excellent for examining the inside of broken pieces of bone, but you can try a vertebra backbone from canned salmon or other fish.

A cross section of muscle meat or beef tendon is easier to cut if soaked twenty-four hours or more in a fixer. These solutions, commonly used in science laboratories, harden the specimen. In the absence of carbon dioxide freezing equipment, also used in laboratories, you will find such tissues as muscles easier to cross-section if quickly frozen in a refrigerator freezer and cut before thawing.

A frog, which has sat in a little water for a few hours, will shed films, strands or flakes of skin into the water. These tissues can be floated with great care onto a slide, arranged with teasing needles and stained with neutral red or other stain. Fish scales of many kinds are easily come by in various ways that will no doubt occur to you. The skin in a tin of canned salmon may reveal some of the interesting color-bearing cells, or chromatophores.
There are many kinds of animal fur to be investigated also even different kinds on the same animal at the same or different times. Tufts, wisps and snips can be acquired in many places, and any fur coat can certainly spare two hairs. Look for shed snakeskins, too. And feathers are among the most absorbing subject try different kinds, and compare the structure of the fluffy down with efficient flight feathers. You may think of many more specimens of animal anatomy to look into than have been mentioned here.