But the nervous system of the amphioxus interests us more than any other part of its body, and the reason is very easily given. An amoeba acts according to what touches it from the outside. In the amphioxus, however, gills, stomach, and muscles are each built up of separate sets of cells. They lie inside the body, and as nothing can possibly touch these cells from the outside, no part can ever tell for itself when to act or how to act. Naturally, therefore, to help them out in their emergency, there must be another set of cells to do the feeling and the directing for them. These special cells must know what is going on at the mouth, in the gills, and on the skin. They must be able to direct the muscles to swim at any needed moment. They must lie close together so as to be able to influence each other and not send opposite commands here and there to the muscles.

Now in the amphioxus there are just such cells doing precisely this sort of work. Moreover, these nerve cells, as they are called, are all bunched together in the walls of the long nerve tube, and they have arms like those of the amoeba, only longer, that reach to mouth and skin and muscle and gill. It is through these arms of the nerve cells that each part of the amphioxus knows what to do and when to do it.

Although each kind of cell in the amphioxus does its own work, nevertheless the whole structure of this headless fish is so very simple that I fear if any other fine

fish, with waving tail, perfect eyes, well-shaped head, and respectable backbone, took notice of such things, it might turn tail and swim away, disowning its poor relation.

We, however, turn tenderly to him because he helps us in trying to understand the growth of the backbone and the nervous system in all vertebrates—ourselves included.

CHAPTER VIII

CELL POISON

After scientists had learned that all living things are either single cells leading independent lives, or groups of cells working together in partnership, they began to ask questions about such other things as may help or hinder the work of the cells.

Alcohol thus came in for its share of attention, and the results were so surprising that newspapers and scientific journals hastened to print them for the world to read.

An experiment in this direction was made with a certain small jellyfish. Its home is in fresh water, and Dr. Richardson chose two from a tank in a botanical garden. Each was put into its own separate jar, and each jar was filled with tank water. In one the water remained as it came from the tank, and the fortunate jellyfish that was put into it moved about in lively fashion, making, on the average, seventy-five motions a minute.

The other jar of water had been specially prepared for the second jellyfish. Into it had been put one drop of alcohol for each thousand drops of water. This innocent-looking compound showed no trace of danger,

and when the little creature was put in, it acted as if it proposed to continue to move at its usual swift speed; but almost immediately its vigor oozed away, its strength failed, its movements grew slower and dragged. In fact

EACH TUBE WAS MOISTENED WITH THE SAME AMOUNT OF
WATER BUT DIFFERENT AMOUNTS OF ALCOHOL

A, pure water; B, one drop of alcohol to 5000 drops of water; C, one
drop of alcohol to 4000 drops of water; D, one drop of

alcohol to 200 drops of water; E, one drop

of alcohol to 100 drops of water

the jellyfish grew weaker so fast that within two minutes it not only ceased to move but sank to the bottom of the jar. It did not suffer, but was evidently paralyzed. At the end of five minutes it seemed so lifeless that Dr. Richardson put it into plain tank water again. Even then, however, the power to swim did not return.

This single jellyfish had taught the great lesson that alcohol, even when mixed with quantities of water, paralyzes groups of living cells.

It seems that other animals are even more sensitive. One drop of alcohol in four thousand drops of water soon kills any water flea that ventures to swim in the mixture.

Dr. Ridge has made experiments with the seeds of the cress plant. He took five glass tubes; put into each the same number of seeds, the same kind and quantity of earth, the same measure of water. This water, however, contained different amounts of alcohol.

Each tube was then sealed, and the picture shows what the difference of growth was in the different tubes.

There is but one explanation for the results. The seeds failed according to the measure of alcohol which they had received.

Ascending the scale of life, even chickens have had to testify about alcohol. Unfortunately for themselves, when the experiment was made they seemed to enjoy the drink. Time and again they hastened to use it; but if they were allowed to take it regularly, even in small quantities, they invariably died of exhaustion or paralysis within six or eight weeks.

They were not so wise as Bum and Tipsy, for, as we know, the dogs objected to alcohol. And yet, just because any poison affects dogs and human beings in