OF ANIMALCULES. 



41 



by a cross, is probably the mouth. It sometimes appears 

 encompassed by a light circle, occasioned by fringes of 

 hair: in a specimen which measured 1- 1200th of an 

 inch in diameter, I could distinctly perceive the ciliae 

 when the creature was at rest. The magnifying power 

 used was about 400. Its motion is various ; sometimes 

 slow, at other times rapid : it is found amongst the 

 small duck- weed {Lemna minor) ^ near the surface of the 

 water. 



30. VoLvox grandinella. The Jwar-frost Volvox, — This 

 animalcule is much smaller than the preceding, and is 

 marked with several circular lines : no internal motion 

 is observable among the opaque molecules. It is irre- 

 gular in its movements ; sometimes swimming in a 

 straight line, at others zig-zag, and often remains in 

 the same spot, producing a tremulous motion. Muller 

 defines them as *' spherical and opaque, with immove- 

 able intestines." It appears to me to be the same species 

 as the pill volvox, in another stage of its growth. 



31. Volvox socialis. The clustered Volvox, — " Spherical 

 volvox, with crystalline molecules, placed at equal dis- 

 tances from each other.'' When much magnified, this 

 animalcule resembles the Vorticella socialis. It consists 

 of several transparent molecules, commonly of a pale 

 brownish-green colour, disposed in a globular cluster : 

 they are of a uniform size, and their outer ends are 

 somewhat conical or egg-shaped. Whether they are 

 inclosed in a common membrane, or united by a stalk, 

 has not been demonstrated, though I am inclined to be- 



