116 THE OCEAN WORLD. 
There are learned men who have composed hundreds of volumes, 
who have published whole libraries—naturalists and physicists who 
have written more than Voltaire ever penned, but whose names are 
almost forgotten. On the other hand, there are some who have left 
only two or three monographs, and yet their names will live for ever. 
Of this number is A. Trembley. This writer published in 1744 a 
“Memoir on the Fresh-water Polyp.” In this little work he recorded 
his observations on some of these animals of the smallest dimensions. 
He limited himself even to two sets of experiments; he turned the 
fresh-water polyp outside in, and he multiplied it by cutting it up. 
These experiments upon this little creature, which few persons had 
seen, have sufficed to secure immortality to his name. Trembley was 
tutor to the two sons of Count de Bentinck. He made his observa- 
tioms at the country-house of the Dutch nobleman, and he had, as he 
assures us, “frequent occasion to satisfy himself, in the case of his 
two pupils, that we can even in infancy taste the pleasures derivable 
from the studies of Nature!” Let us earnestly hope that this 
thought, uttered by a celebrated naturalist, who spoke only what 
he knew himself, may remain engraved on the minds of our younger 
readers. 
Trembley established by his observations, a thousand times repeated, 
that Hydra viridis can be turned outside in as completely as a glove 
may be, without injury to the animal, which a day or two after this 
evolution resumes its ordinary functions. Such is the vitality of these 
little beings, that what was once the outer surface soon fulfils all the 
functions of a stomach, digesting its food, while the intestinal tube, 
expanding its exterior, performs all the functions of an outer surface, 
it absorbs and respires. But we shall leave Trembley to relate his very 
remarkable experiments. 
“T attempted,” he says, “ for the first time to turn these polyps 
inside out in the month of July, 1741, but unsuccessfully. I was 
more successful the following year, having found an expedient which 
was of easy execution. I began by giving a worm to the polyp, 
and put it, when the stomach was well filled, into a little water 
which filled the hollow of my left hand. I pressed it afterwards with 
a gentle pinch towards the posterior extremities. In this manner I 
pressed the worm which was in the stomach against the mouth of 
the polyp, forcing it to open—continuing the pinching pressure until 
the worm was partly pressed out of the mouth. When the polyp was 
in this state I conducted it gently out of the water, without damaging 
it, and placed it upon the edge of my hand, which was simply mois- 
tened in order that the polyp should not stick to it. I forced it to 
