Natural History of British Zoophytes. 331 



that this species is not identical either with the Hydra lutea or cory- 

 naria of Bosc. 



Obs. Leuwenhoek * discovered the Hydra in 1703, and the un- 

 common way its young are produced, and an anonymous correspon- 

 dent of the Royal Society made the same discovery in England about 

 the same time, but it excited no particular notice until Trembley 

 made known its wonderful properties, about the year 1744. These 

 were so contrary to all former experience, and so rejmgnant to every 

 established notion of animal life, that the scientific world were amaz- 

 ed ; and while the more cautious among naturalists set themselves 

 to verify what it was difficult to believe, there were many who looked 

 upon the alleged facts as impossible fancies. The discoveries of 

 Trembley were, however, speedily confirmed ; and we are now so 

 familiar with the outlines of the history of the fresh-water polype, 

 and its marvellous reproductive powers, that we can scarcely appre- 

 ciate the vividness of the sensation felt when it was all novel and 

 strange ; when the leading men of our learned societies were daily 

 experimenting on these poor worms, and transmitting them to one 

 another from distant countries, by careful posts, and as most precious 

 gifts ; and when even ambassadors interested themselves in sending 

 early intelligence of the engrossing theme to their respective courts. 



The Hydrse are found in fresh and, perhaps, also in salt waters, but 

 the former species only have been examined with care, and are the 

 'objects of the following remarks. They prefer slowly running or al- 

 most still water, and fasten to the leaves and stalks of submerged 

 plants by their base, which seems to act as a sucker. The body is 

 exceedingly contractile, and hence liable to many changes of form : 

 when contracted it is like a tubercle, a minute top or button, and 

 when extended it becomes a narrow cylinder, being ten or twelve times 

 longer at one time than at another, the tentacula suffering changes in 

 their length and diameter equal to those of the body. " It can lengthen 

 out or shorten its arms, without extending or contracting its bodv ; 

 and can do the same by the body, without altering the length of its 

 arms : both, however, are usually moved together, at the same time 

 and in the same direction." — The whole creature is apparently homo- 

 geneous, composed of minute pellucid grains cohering by means of a 

 transparent jelly, for even with a high magnifier no defined organi- 

 zation of vessels and fibres can be detected. On the point opposite 

 the base, and in the centre of the tentacula, we observe an aperture 



* " Antonius v. Leeuwenhoek, civis Delpbensis, petitus vitiorum politor, 

 curiosus, et ad paradoxas opiniones pronus." Haller, Bib. Bot. i. 583. He 

 was born 1632; elected F. R. S. January 1680 ; and died in 17*23. 



