ROTATORIA. 149 



of which is covered with sheet cork, into which the 

 pins are stuck. 



The smaller beetles, &c., which cannot be trans- 

 fixed with a pin, may be mounted as opake objects 

 upon slips of card, the legs &c., being carefully 

 spread out, and gummed in position with a strong 

 solution of gum-tragacanth in boiling water. Many 

 of the smaller Curculion'idse or diamond-beetles, in 

 which the labium forms a rostrum or beak, with 

 elbowed or half-bent antennae, form beautiful opake 

 objects when thus mounted, on account of the brilliant 

 scales with which they are covered. 



There are two ways of examining insects either in 

 the entire state as opake objects or the separate parts 

 mounted as transparent objects. In the former case 

 the pin with which the insect is transfixed should be 

 stuck into a slide made of cork, and this laid upon 

 the stage, or the pin may be held by the forceps. In 

 this way, with the use of the side condenser and a 

 low power, the general form and arrangement of the 

 parts of the insect can be made out. The more 

 minute details must be searched for in the individual 

 organs which have been picked off with forceps, and 

 mounted in balsam. 



If it be required to submit the parts of a dried 

 insect to examination, this must be previously soaked 

 in warm water for a time, as the legs, &c., become 

 very brittle when dry, and are thus easily injured. 



ROTATOR IA (rota, a wheel) or ROTIF'ERA (rota and 

 fero, to bear). The animals contained in this class 

 are minute, being just distinguishable to the naked 

 eye as white specks. They are common in long-kept 

 infusions and among Conferva in the water of pools 

 and ditches. Their body is usually longer than broad, 

 often presenting indications of rings ; and at or near 

 the posterior end is frequently found a prolongation 

 resembling a tail, but terminated by two short move- 

 able thumb-like processes, rarely a sucker, which 



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