92 HABITS AND INSTINCTS OP ANIMALS. CHAP. IV. 



ground. All these states are subject to different modifi- 

 cations ; and these several peculiarities it will now be 

 our business to detail. 



(111.) The minute tribes forming the Acrita may 

 be first noticed ; and, here, how endless is the diversity 

 of motion among a class of beings scarcely perceptible 

 to our vision, and infinite numbers of which mock the 

 most ingenious efforts of art to discover. The motions 

 of those animalcules which are unattached, are singularly 

 varied ; and, among these, we may notice two species 

 of Forticella the rotatoria and the conveUaria. The 

 latter, to the naked eye, has the appearance of a small 

 white speck ; but, when examined through a microscope, 

 it resembles a small bell-shaped flower: it is seen, every 

 now and then, to contract its stem, with a kind of con- 

 vulsive motion, into a spiral form ; and again returning, 

 in a short time, to its former length.* The Vibrio 

 Proteus an animalcule found in the slimy matter which 

 coagulates upon the side of a vessel, the water in which 

 has been impregnated with some animal or vegetable 

 substance will swim about with great vivacity. Some- 

 times it makes a stop for a minute or two, and stretches 

 itself out, apparently in search of prey. When alarmed, 

 it immediately draws in its neck, becomes more opaque, 

 and moves sluggishly. It will then, perhaps, instead 

 of its former long neck, push out a kind of wheel ma- 

 chinery, the motions of which draw a current of water, 

 and along with this, probably, its prey. Withdrawing 

 the wheel, it will sometimes remain almost motionless 

 for one or two seconds, as if weary ; then, protruding 

 its long neck, wilt often resume its former agility, or 

 adopt, in succession, a multitude of different appear- 

 ances, f The Volvox Globator moves its little body 

 over and over, spinning like a top, or sometimes moving 

 calmly along without turning round ; while the Volvo x 

 Bulla, which is scarcely visible to the naked eye, pre- 

 sents, under the microscope, a series of movements of 

 the most curious and unceasing variety. 



* Bing. Anira. Biog. vol. iii. p. 490. t Id. ibid. p. 493. 



