BIOLOGY. 319 



days, exposed to the air and to the light, at the end of that time 

 the water will have assumed a green, or brownish-green tinge, 

 and, on being submitted to examination under the microscope, 

 will be found to swarm with many descriptions of infusoi"ia. How 

 did they come there? Some say their eggs, or " buds," are con- 

 stantly present in the air, driven about everywhere by the wind, 

 and develop themselves whenever they hajiijen to fall upon an 

 approjDriate medium, such as putrefying vegetable substances. 

 Others say that the eggs form spontaneously in water containing 

 vegetable matter, as the eggs of other animals in the womb. 



Naturalists, such as Lamarck, Oken, Geoifroy St. Hilaire, Dar- 

 'win, and others, consider infusoria (^Monads) as the fundamental 

 organic substance from which all higher organisms have been pro- 

 gressively developed. Nature created Monads, the most simple 

 form of infusoria, from the gradual perfection of which, through 

 myriads of centuries, and amidst all kinds of physical changes, 

 all the higher classes of animals have been produced. On such 

 points, while we may persistently investigate, we may reserve our 

 judgment. 



The Monad, the simplest form of infusorial life, consists of a 

 fine pellucid membrane ; it forms a very minute sphere or cell, 

 having a few green or colored spots in its interior. It requires to 

 be magnified 610 times to be seen at all. Some authors say it 

 varies from 1-24,000 to l-500th of an inch in size, according 

 to the species. According to Humboldt, the true monad never 

 exceeds 1-3, 000th of a line in diameter. It effects its locomotion 

 by means of cilia, fine hair-like processes which cover the whole 

 sui"face of the body, and which are constantly vibrating. 



Some of the infusorial animalcula secrete a covering of hard 

 flint ; so that the covering of infusoria is of two kinds : the one 

 soft and ajiparently membranous ; the other rigid and hard, hav- 

 ing the appearance of a shell, though, from its iiexibilty and trans- 

 parent nature, it is more like horn. The microscopic beings be- 

 longing to the class of Rhizopoda — a class higher than infusoria 

 — present also the latter peculiarity. This hard covering consists 

 sometimes of silica, and sometimes of carbonate of lime. To it 

 we owe the preservation of infusoria and foraminifera which have 

 lain for centuries upon centuries in a fossil state, in the strata of 

 the earth. It has been calculated that eight million individuals of 

 Monas crepusculum can exist within the space that would be occu- 

 pied by a grain of mustard-seed, the diameter of which does not 

 exceed one-tenth of an inch. The rapid and mysterious transition 

 of color which is observable in lakes, and which has often created 

 alarm in the minds of the superstitious, has been attriljuted to 

 infusoria. A lake of clear, transparent water will assume, for 

 instance, a green color in the course of the day, it will become 

 turbid or mud-colored about noon, when the sun brings the infu- 

 soria to the surface, rapidly develops them, and where they die 

 by millions before night. Microscopic vegetables may produce 

 similar results. Infusoria and rhizopoda play an important 

 part in the phosphorescence of the sea. The luminosity of the 

 waves is supposed to be entirely due to them. 



