DIFUSORtA. t 



difficulty ; and the word once known, it is not readily forgotten. 

 In the preceding instance, we have explained the meaning of 

 the words Polygastrica and Rotifera, so that we hope there 

 will not be anythmg difficult or obscure in their use hereafter. 

 We shall endeavour to do the same with such oflher scientific 

 terms as we may have occasion to employ. Their number is 

 few, and they are of such great utility that the acquisition of 

 them is worthy of a little eftbrt. By such means we can 

 indicate to a person in a remote country, and speaking a foreign 

 language, the very animal regarding which we have any fact 

 to communicate; and, in like manner, we can know with 

 certainty of what animal observations made in other parts of 

 the world are recorded. The terms of science are common to the 

 men of science in all countries ; and, if the terms be correctly 

 applied, no doubt or ambiguity can arise. They furnish us 

 with the means of expressing the ideas we wish to convey, 

 with a precision otherwise unattainable ; and the habitual use 

 of them assists in giving precision to the ideas themselves, and 

 thus forms a help in that mental process which the mind of 

 the naturalist must undergo in the acquisition of knowledge. 



It may naturally be asked how, in beings so inconceivably 

 minute as the Polygastrica, the existence of a number of sto- 

 machs could be discovered. The plan adopted by Ehrenberg 

 for this purpose was ingenious : — The professor removed some 

 of them from the water in which they were found, and placed 

 them in water of the purest and most transparent description, 

 and, after having subjected them, to a fast for some time, he 

 put into it an infusion of indigo or carmine which tinged the 

 water. When they began to feed, he found, as the stomachs 

 filled, they became visible by the blue or red particles shining 

 through their transparent skins. The bodies of the Poly- 

 gastrica are furnished with fine hair-like appendages, termed 

 cilia;* these are scattered over the surface, and by their 

 continual movement propel the little animals through the 

 water, and bring within their reach the particles of decaying 

 vegetable matter on which they live. There is reason to 

 believe that these singular organs of locomotion are not put 

 into activity by the will of the animal; and hence that their 

 movement, like that of the human heart, might continue for 

 any length of time without inducing a feeling of fatigue. This 



• Tlie Latin word for eyelashes. 



