269 
HYDR2E, OR FRESH-WATER POLYPES, 
and others, extended our acquaintance with these interesting 
polypifera, whose animal nature is, of course, now known to all 
naturalists. I have given this brief historical sketch, because 
we learn from it that Trembley's discovery of the fresh-water 
hydrse, whose animal nature was so apparent, was the very 
circumstance that turned the tide of disputation about the 
corallines in favour of Peyssonnel' s opinion, as well as because 
it is instructive to watch, as it were, the gradual development 
of a new doctrine, its severe birth-pangs, and its final acceptance 
as truth. 
As has been stated, Leeuwenhoek was the first discoverer of 
the hydra, and of the manner in which the young are produced 
by gemmation. He noticed the great contractility of the 
animal's tentacles, and he sent a letter to the Royal Society, 
dated December 25, 1702, which may be read in vol. xxiii. 
pp. 1304 — 1311 of the Philosophical Transactions. This 
communication attracted little notice at the time, and seems 
to have been forgotten when Trembley announced his startling 
discoveries. Leeuwenhoeks letter to the Royal Society was 
dated 1702, as has been already stated; Peyssonnel was 
born in 1700; Reaumur's notice of Peyssonnel' s assertion of 
the animal nature of coral was made to the French Academy 
of Sciences in 1727 ; that is to say, twenty-five years after 
Leeuwenhoek's letter. Trembley drew the attention of the 
learned world to his experiments with the hydra about the 
year 1744. We have seen how these experiments turned 
the tide in favour of Peyssonnel's opinion ; it is highly 
probable that Leeuwenhoek's communication, with the figure 
he has given, would have helped to settle the question as to 
the animal nature of corals some years before Trembley 
wrote, had the Dutch naturalist published his account of 
the hydra after the year 1727 instead of before it. However, 
it is satisfactory to know that Peyssonnel lived to see a 
change of opinion in his favour, and to find De Jussieu and 
Reaumur his hearty advocates. The excitement amongst 
naturalists that followed Trembley's discoveries of the . extra- 
ordinary properties of the hydra was intense. That an 
animal should be chopped into several pieces, and that 
each part should survive and the creature increase under 
the operation, that a veritable animal should bud out young 
ones after the manner of plants, that whether its body 
were turned inside or outside it made no difference, that 
portions of one individual could be grafted into portions 
of another, — all these things were so contrary to established 
experience and to all then known physiological laws that 
many would not believe them. And so the sceptics — and 
scepticism in science is a virtue — experimentalized themselves 
