178 DROPS OF WATER. 



with a disc at the end, by which it holds to sub- 

 stances : it proceeds from near the centre of the 

 under surface of the lorica, and is clearly seen 

 when the creature turns on its side, which it does 

 frequently in swimming. It has two eyes. 

 When alarmed, it withdraws its wheels into the 

 case, as well as the tail, nearly, and lies quite still 

 for a moment, soon, however, becoming active 

 again, and then nothing can be more inter- 

 esting than the quiet movement and elegant 

 appearance of this animalcule. It is not com- 

 mon, but found sparingly in summer, principally 

 among Lemna ; I once found it as early as 

 February, but in small numbers. P. ettiptica 

 has a lorica of an elliptical form. P. clypeata is 

 found in sea- water: it has an oblong lorica, 



