126 ANTHOZOA HYDROIDA. 



the Boyal 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 repugnant to every 

 established notion of animal life, that the scientific world were 

 amazed ; and while the more cautious among naturalists set them- 

 selves to verify what it was difficult to believe, there were many 

 who looked upon the alleged facts as impossible fancies. The dis- 

 coveries 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 appreciate 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 them- 

 selves in sending early intelligence of the engrossing theme to their 

 respective courts.* 



The Hydrse are found in fresh waters only. They prefer slowly 

 running or almost 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 ten- 

 tacula suffering changes in their length and diameter equal to those 

 of the body. " It can lengthen out or shorten its arms, without ex- 

 tending or contracting its body ; 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." On the point opposite the base, and in the centre of the 

 tentacula, we observe an aperture or mouth which leads into a 

 wider cavity, excavated as it were in the midst of the body,t and 



* Hence the inquiry became an object of ridicule with our popular writers. See 

 Goldsmith's Citizen of the World, letter 89. What saith posterity ? " Trembley 

 acquit une reputation universelle par sa decouverte extraordinaire, qui changeait, 

 pour ainsi dire, toutes les idees qu'on avail cues sur la physiologic et 1'anatomie ani- 

 males." Who is this partial judge? His decisions may have been favourable ; but 

 who shall accuse Georges Cuvier of injustice ? See his Hist, des Sciences Nat. iii. 

 p. 256. 



f Pallas denies this. " Ab alimento recepto cavata, inquam, hand enim Hydrae 



