HYDRA. 189 



it fast till the polype can master and devour it. This is 

 by far the most common Hydra in the west of Scotland. 

 It is so common, indeed, that if in summer or autumn you 

 take up at random a handful of duckweed or pond-weed 

 (Lemna or Potamogeton) from a ditch or stagnant pool, and 

 put it in a glass vase, you are almost sure to see that you 

 have captured several green Hydrce. Their tentacula, 

 however, though not some inches long, like those of other 

 species figured by Trembley, can be extended by the creature 

 so as to be fully the length of the body. " I imagined those 

 polypes owed their green colour to some particular food, such 

 as weeds, etc., and that they would lose it upon being kept 

 to worms ; but I find myself mistaken, for they retain their 

 greenness after some months as well as ever, and are now 

 grown of a moderate size, extending sometimes three- 

 quarters of an inch; their tentacula are also lengthened 

 very much to what they were, and are of a lighter green 

 than the body, their number, eight, nine, or ten. The tail 

 is very little slenderer than the body, but more spread at 

 the end than the tails of the other kinds." (Baker, 1743.) 

 Pallas says, that the offspring are produced from every part 

 of the body. Blainville thinks he has remarked that they 

 spring always from the same place, though he owns that 



