176 THE MICROSCOPE. 



Before quitting the consideration of the Protozoa, we must refer 

 to a curious group of minute parasitic creatures, the genus Gregarina, 

 of which we know six distinct species, all of them Entozoa, and all 

 organised as simple cells, but endowed with contractility and expansi- 

 bility quite sufficiently to put their animal nature beyond a doubt, and 

 which appear to be more nearly allied to the Infusoria than to any 

 other class in the animal kingdom. They are to be found in the intes- 

 tines of the common garden worms, insects, and many other members 

 of the articulate division of animals, and are but rarely to be met with 

 in animals of any other group. These animals are generally of a cylin- 

 drical or somewhat elliptical form, although sometimes a sort of head 

 appears to be produced by the constriction of the anterior extremity 

 of the body, and this head-like portion is occasionally furnished with a 

 curious soft process and lobes. They are very sluggish in their move- 

 ments, although a few possess true cilia. Their curious mode of deve- 

 lopments, with other points in the history of these minute parasites, 

 are well worthy of investigation. 



We have taken a rapid survey of some of the marvellous creations 

 in the busy invisible world ; every glimpse inspiring awe, from the im- 

 mensity, variety, beauty, and minuteness of the organised habitants. 



Immensity, in its common impression on the mind, hardly conveys 

 the idea of the myriads upon myriads of Infusoria that have lived and 

 died to produce the tripoli, the opal, the flints, the bog-iron, ochre, and 

 the limestone of the world. 



Professor Owen beautifully explains the uses of this vast amount 

 of animalcule life : 



" Consider their incredible numbers, their universal distribution, 

 their insatiable voracity ; and that it is the particles of decaying vege- 

 table and animal bodies which they are appointed to devour and assi- 

 milate. Surely we must, in some degree, be indebted to these ever- 

 active, invisible scavengers, for the salubrity of the atmosphere and 

 the purity of water. Nor is this all ; they perform a still more im- 

 portant office in preventing the gradual diminution of the present 

 amount of organised matter upon the earth. For when this matter is 

 dissolved or suspended in water, in that state of comminution and 

 decay which immediately precedes its final decomposition into the ele- 

 mentary gases, and its consequent return from the organic to the inor- 

 ganic world, these wakeful members of nature's invisible police are 

 every where ready to arrest the fugitive organised particles, and turn 

 them back into the ascending stream of animal life. Having converted 

 the dead and decomposing particles into their own living tissues, they 



