ORGANS OF DIGESTION. 305 



ties of form manifested by the organs of animal life, and 

 with all the living habits and instincts of animals. 



SECOND SECTION. 



Digestive Organs of the Cyclo-neurose, or Radiated Classes. 



In the lowest tribes of animals the internal organization 

 relates almost solely to digestion, and the food consists 

 almost entirely of the simplest forms of animal matter. The 

 alimentary cavity has often but one orifice, it is seldom 

 provided with masticating organs, and scarcely a trace of 

 &ny glandular organ is yet observed to assist in the process 

 of assimilation. Like the exterior form of the body, the 

 digestive apparatus is more varied in this than in any of the 

 higher divisions of the animal kingdom. 



I. Polygastrica. Internal digestive cavities are seen in 

 the simplest monads ; and they are so numerous in almost 

 all the higher forms of animalcules, that the class has been 

 termed polygastrica from this character. From the great 

 transparency of these microscopic animals, their digestive 

 sacs, when empty, or when filled only with water as they 

 often are, appear like portions of the common cellular 

 substance of the body, or like gemmules, or internal animaU 

 cules, and from not being easily or generally recognised as 

 alimentary cavities, many, like Lamarck, were led to believe 

 that these animals were without a mouth or any internal or- 

 gans, and were nourished by superficial absorption, like marine 

 plants. Lewenhoeck, however, observed that they possessed 

 an internal cavity, and devoured each other ; the same was seen 

 by Ellis ; Spallanzani perceived them swallowing each other 

 so voraciously that their bodies became distended with their 

 prey ; and Goetze designated the trichoda cimex the wolf of 

 infusions from its rapacity among the smaller animalcules. 

 Gleichen placed animalcules in infusions coloured with 

 carmine in order to discover the forms of their digestive 

 cavities, and he has figured many trichocke, vorticella, and 



TART III, X 



