INFUSOKIA. 103 



the extreme simplicity of structure in the Infusoria has, however, 

 met with much opposition. To accord them neither four nor two 

 stomachs, it is not necessary to deprive them of the organ altogether. 

 Meyen represents them as having one great hollow stomach occupied 

 by a pulpy matter, into which the alimentary masses are successively 

 absorbed. " All recent observations," says Milne Edwards, " tend to 

 establish the fact that the digestive apparatus of the ciliate Infusoria 

 consists of first, a mouth ; second, of a pharyngeal canal, in which the 

 food often assumes the form of a bolus ; third, of one great stomach 

 with distinct walls, and more or less distant from the common tegu- 

 mentary membrane ; fourth, of an excretory orifice." 



This mouth presents sensible differences both as to its position and 

 conformation, often occupying the bottom of a hollow, the edges of 

 which are furnished with well-developed cilia, the action of which 

 attracts the aliment ; in short, the mouth is a sort of decoy at the 

 bottom of a simple pit, being at once contractile and prehensile, the 

 interior part being sometimes capable, according to Milne Edwards, of 

 being turned inside out in the form of a trumpet, while in a great 

 many species it is provided with a peculiar armature, consisting of a 

 band of rigid bristles disposed in the form of a bow-net, and suscep- 

 tible of dilatation and contraction, according to the wants of the 

 animal. The oesophagus, which is connected by means of the canal 

 with the mouth, has generally an oblique direction backwards, often 

 terminating in a great undivided stomach. 



The reproduction of the Infusoria exhibits some very surprising 

 phenomena, while it offers another proof of the wonderful means 

 Nature employs for perpetuating the races of animals. They can be 

 reproduced by three different processes : 1. By gemmation, or budding, 

 somewhat after the manner of plants. 2. By sexual reproduction ; for 

 in these little creatures it has recently been discovered that sexual 

 differences exist. 3. By the spontaneous division of the animal into 

 two individuals a process known to zoologists as fissiparism or fission. 



Among these three processes, that which appears best understood is 

 the last. The singular phenomenon of spontaneous division may be 

 witnessed by any one having patience to examine the creature long 

 enough, isolated from its innumerable companions, under the micro- 

 scope. The oblong body of the animal will soon be observed to con- 

 tract at the middle, the compression becoming more and more marked. 



