102 ZOOLOGICAL PHILOSOPHY 



a shape which has long caused these groups to be taken for true plants, 

 since they are often branched almost in the same way. 



Whether polyps have one or several mouths, there is always an 

 aUmentary canal to which they lead and consequently an organ for 

 digestion, of which all plants are destitute. 



If the degradation of organisation that we have observed in all classes 

 starting from the mammals is anywhere obvious, it is assuredly among 

 the polyps, whose organisation is reduced to an extreme simphfication. 



INFUSORIANS. 



Infinitely small animals with gelatinous, transparent, homogeneous 

 and very contractile bodies ; with no distinct special organ internally, 

 but often oviform gemmules ; and having externally no radiating 

 tentacles nor rotatory organs. 



At length we reach the last class of the animal kingdom, comprising 

 the most imperfect animals from all points of view ; that is, those 

 which have the simplest organisation, possess the fewest faculties and 

 seem all to be mere rudiments of animal nature. 



Hitherto I have placed these small animals in the class of polyps, 

 of which they constituted the last order under the name of amorphous 

 polyps, since they have no constant shape pecuhar to them all ; 

 but I have recognised the necessity of separating them to form a class 

 apart, though this in no wise changes the rank that I had assigned 

 to them. The only result of this change is to establish a Une of demarca- 

 tion which appears to be called for, on account of the greater sim- 

 plicity of their organisation and their lack of radiating tentacles and 

 rotatory organs. 



Since the organisation of the infusorians becomes ever more simple 

 as we pass down their genera, the last of these genera shows us in some 

 degree the limit of animahty, the hmit at all events of what we can 

 reach. It is especially in the animals of the second order of this class 

 that we can verify the entire disappearance of any trace of an intestinal 

 canal and mouth ; so that they have no special organ whatever nor 

 any digestion. 



They are only very tiny gelatinous, transparent, contractile and 

 homogeneous bodies, consisting of cellular tissue, with very shght 

 cohesion and yet irritable throughout. These tiny bodies, which look 

 like animated or moving points, feed by absorption and continual 

 imbibition ; and they are doubtless animated by the influence of the 

 subtle surrounding fluids, such as caloric and electricity, which stimu- 

 late in them the movements constituting life. 



