76 VIEWS OF THE MICROSCOPIC WORLD. 



different in form and smaller than the first. The third sort is also oviparous, 

 Fig. us. and is exhibited in figure 114. In figure F . m 



115 three extremely small eels are shown, 

 which are specimens of the fourth class. 



The manner in which these animals 

 originate has given rise to much discus- 

 sion, inasmuch as they are not only found 



to be viviparous ; but are also said to be produced when the paste is 

 covered. An opinion has therefore been entertained that their origin 

 is spontaneous ; a circumstance which would be at variance with all 

 our experience. Dr. Ehrenberg, in respect to Infusoria, has experimented for 

 many years with pure spring water, distilled water, and rain water ; with and 

 without vegetables, boiled and unboiled, and always with the following results ; 

 that when open vessels were exposed to the air animalcules were discovered after a 

 longer or shorter time, according to the temperature, and other attendant cir- 

 cumstances ; but if the vessels were closed, infusorial life was rarely detected. 

 In view of these facts it may be inferred, that when eels are said to have been 

 found in paste that was covered, that sufficient precautions had not been adopted 

 to exclude it entirely from all access of the atmosphere, and that invisible eggs or 

 germs, like those of Infusoria, were either contained in the air that floated at 

 first above the pa.ste in the jar, or were borne upon slight currents into the vessel, 

 through minute apertures that escaped observation. 



The fact that the eels of paste are viviparous cannot fairly be urged as an 

 argument against their generation from a known cause, inasmuch as the same 

 individual is both oviparous and viviparous ; six young eels and twenty-two 

 eggs having been found in a single specimen at one time. In their modes of 

 increase they therefore resemble numerous species of Infusoria, which are not 

 confined to one method of production, but multiply in various ways. 



THE VINEGAR EEL. If a small quantity of good vinegar is viewed in a wine- 

 glass, by the naked eye, under a strong light, the fluid will generally be seen 

 filled with slender threadlike bodies in rapid motion. These are the eels of 

 vinegar, which, when studied under the microscope, are found to be larger than 

 the Paste eel but not so thick ; the tail is also smaller, more tapering, and 

 moves with greater rapidity. Like the Paste eel they increase by eggs, and also 

 bring forth their young alive. The eels of vinegar are finely displayed when a 

 little reservoir is made between two narrow slips of glass, and the cavity filled 

 with a few drops of vinegar. If the fluid is then magnified by the solar micro- 

 scope, and its image received upon a large screen, hundreds of eels, apparently 

 more than a foot in length, will be seen upon the screen in the highest state of 

 activity, crossing and recrossing its surface, and darting and twisting in every 

 direction. Sometimes if a small piece of mother floats in the vinegar, several 

 eels will become entangled in it at the same time, and their rapid evolutions as they 

 struggle to escape from this impediment affords an interesting spectacle. Their 



