Microscopical Essays. 1^3 



more eafily perceived in a ditch when the fun mines on the bot- 

 tom, than at another time. They are feldom to be met with in 

 winter : about the month of May they begin to appear and 

 increafe. 



They are generally to be found in waters which move 

 gently; for neither a rapid ft ream, nor ftagnant waters, ever 

 abound with them. As they are always fixed to fome fubftance 

 by their tails, and are very rarely loole in the water, taking up 

 water only can fignify but little ; a circumftance which has pro- 

 bably been the caufe of much difappointment to thofe who have 

 fearched for them. 



The green polypes are generally about half an inch long when 

 firetched out ; thofe of the fecond and third fort are between 

 three quarters of an inch and an inch in length ; though fome 

 are to be found at times w hich are an inch and a half long. 



Heat and cold has the fame effecl upon thefe little creatures, 

 that it has upon thofe of a larger fize. They are animated and 

 enlivened by heat, whereas cold renders them faint and languid ; 

 they mould therefore be kept in fuch a degree of heat, that the 

 water may not be below temperate. 



It is convenient for many experiments to fufpend a polype 

 from the fur face of the water. To effect- this, take a hair pencil 

 in one hand, and hold a pointed quill in the other; with the 

 pencil loofen the polype from the receiver in which it is kept, 

 and gradually raife it near the t op of the water, fo that the ante- 

 rior end may be next the point of the pencil; then lift it out of 



U the- 



