INFUSORIAL ANIMALCULES. 15 



should this test, however, be deemed unsatisfactory, press 

 down the cover of the aquatic live- box, so as to crush the 

 specimens, when the coloured fluid will enter and surround 

 their bodies, and by a proper management of the illumina- 

 tion of your microscope, the broken edges of the lorica 

 will be visible, as seen in fig. 33, which is a representation 

 of the Trachelomonas volvocina similarly circumstanced. 



Until recently, many of the genera of the smaller kinds 

 of animalcules were supposed to be devoid of any external 

 organs whatever ; but the feeding on coloured substances, 

 and introduction of achromatic glasses, has proved the 

 incorrectness of this conclusion, even as respects the 

 Monads. The simplest external member, observable in 

 the Infusoria, is a single, delicate, hair-like filament, situate 

 near the oral orifice or mouth, and which has, conse- 

 quently, been designated the proboscis. When this 

 member is of an uniform appearance, it is said to be 

 filaform, or thread-like ; but, when it tapers toward the 

 extremity, like an eye-lash, or cilium, it is denoted flagel- 

 liform. This organ is used by the animalcule both for 

 locomotive and purpeying purposes. When the creature 

 is in rapid motion through the water, this instrument acts 

 as an oar or paddle, in facilitating a progressive movement, 

 whilst, at the same time, a current is created in the direc- 

 tion of its mouth, for the procuration of food. This 

 member is not easily seen, inasmuch as considerable skill 

 in the use of the microscope is required to shew it, nor 

 will even that, in all cases, succeed. The employment of 

 finely- divided indigo or carmine affords the surest proof 

 of its existence. When, by this means, its action has been 

 detected, allow the water to evaporate, and you may notice 



