HYDRA. Lit 
Memoirs, published at the Hague, in 1743, entitled ‘ Mé- 
moires pour servir 4 histoire d’un genre de Polypes d’eau 
douce, & bras en forme de cornes;’ and also ‘ Baker’s 
Natural History of the Polype,’ published likewise in 
London, in 1743. What renders M. Trembley’s work much 
more valuable is, that it is illustrated with many plates, and 
these from the pencil and the burin of the highly celebrated 
engraver Lyonet. M. Trembley, of Geneva, tells us in his 
Memoir, that in the summer of 1740, when he made these 
discoveries, he was residing at Sargoliet, the country-house 
of the Comte de Bentinck, at a little distance from the 
Hague. Having taken up some water-plants from a ditch, 
and placed them in a glass vessel, his curiosity was excited 
by the numerous animalcules with which the water became 
filled. While engaged in examining them, his eyes casually 
lighted on a polype attached to a branch of the water-plant; 
but he paid little attention to it, as, being expanded and 
motionless, he thought it a little parasitical plant. Please 
to look at the figure of the expanded Hydra, and you will 
see the form in which it at first presented itself to him. 
Looking at it afterwards, he observed some motion in what 
we now call the tentacula or feelers, but he ascribed this to 
the motion of the water, occasioned, he conjectured, by the 
