OF MICR O- ORGANISMS. 67 



cipient traces of such aesthetical manifestations point- 

 ing towards the preparation of two animals for sexual 

 intercourse. 



" It is curious," remarks M. Balbiani, " to find 

 among these organisms which all zoologists, by reason 

 of their diminutive size and extreme simplicity of 

 structure, have placed at the remotest limit of the animal 

 kingdom, acts that mark the existence of phenomena 

 analogous to those by which the sexual instinct is ex- 

 hibited in a large number of Metazoans. Upon the 

 approach of the period for propagation, the Paramecia 

 come in from all points of the fluid and assemble like 

 little whitish clouds in more or less numerous groups 

 about the objects that float upon the surface of the 

 water, or adhere to the side of the vessel containing 

 the tiny artificial sea in which the animalcula are held 

 captive. Intense excitement, which the need of food 

 does not suffice to explain, prevails in each of these 

 groups; a higher instinct appears to dominate all these 

 tiny organisms; they seek each other's company, chase 

 each other about, feel here and there with their cilia, 

 adhere for a moment or so in an attitude of sexual co- 

 ition, and then retire, soon to begin anew. When 

 these minute assemblages are dispersed by shaking 

 the liquid, they quickly form again at other points. 

 These singular antics wherewith animalcula appear 

 to incite each other mutually to copulation often 

 continue for several days before the latter act is defin- 

 itely effected. 



" Other Infusoria, particularly the Spirostomes, seek 

 the deep spots of the liquid, or bury themselves in the 

 oozy sediment of the bottom, not to come forth again 

 until they have separated. The Stentors have differ- 

 ent habits. They are affixed by their pedicles to sub- 



