Microscopical Essays. 



401 



Whoever has looked with care at the bottom of a wet (hallow 

 ditch, when the water is ftagnant, and the fun has been powerful,, 

 may remember to have feen many little -tranfparent lumps, of a 

 jelly-like appearance, about the fize of a pea, and flatted on one 

 fide ; the fame appearances are alfo often to be feen on the under 

 fide of the leaves of thofe weeds, or plants, that grow on the furface 

 of the water ; thefe are the hydra, gathered up into aquitfcentftate, 

 and feemingly inanimate, becaufe either undifturbed, or not ex- 

 cited by the calls of appetite to action. They are generally fixed 

 by one end to some iohd fubllance, at the other end there is a 

 large opening, round about which the arms are placed as fo 

 many rays round a cent r, which center is the mouth. 



They are (lender and pellucid, formed of a kind of tender fub- 

 ftance, in confidence fomething like the horns of a mail, and can 

 contract the body into a very (mall compafs, or extend it to a 

 confiderable length. They can do the fame with the arms ; with 

 thefe they feize minute worms and various kinds of aquatic in feels, 

 bring them to the mouth and fwallow them. After the food is 

 digefted, and the nutritive parts which are employed in fuftaining 

 it's life are feparated from the reft, they reject the remainder by 

 the mouth. 



The firfl polype which Mr. Trembley difcovered was one of 

 the hydra viridis, reprefented at Fig. 5, Plate XXI. Thefe are 

 generally of a fine green colour. The indications of fpontaneous 

 motion were firft perceived in the arms of thefe little creatures ; 

 they can extend or contract, bend and wind them divers ways. 

 Upon the flighted, touch they contract themfelves fo much, as to 

 appear little more than a grain, of a green fubllance, the arms 



3 C difap- 



