334 ORGANS OF DIGESTION. 



THIRD SECTION. 



Digestive Organs of the Diplo-neurose or Articulated 

 Classes. 



The lengthened cylindrical and articulated form of the 

 body in the helminthoid and entomoid classes, is that best 

 suited for the creeping, piercing, parasitic and carnivorous 

 habits, so characteristic of this great division of the ani- 

 mal kingdom, and the internal organs of these animals, 

 especially the digestive, partake of this straight and ex- 

 tended form of the trunk. In the radiated animals, which 

 are almost all stomach, the shortness and the vertical 

 position of the axis, and the lateral expansion of the 

 alimentary cavity, often enable them to dispense with a 

 second orifice to their digestive sac, and better adapt them 

 for seizing and swallowing entire the smaller animals so 

 numerously spread through the waters of the globe. The 

 carnivorous character, so general in the articulated classes, 

 and even the highly organized condition of their prey, are 

 indicated by the limited capacity and by the short and 

 straight course of their alimentary canal, which almost uni- 

 versally opens at the two opposite extremities of the body, 

 and by the numerous prehensile and destructive instru- 

 ments so commonly placed at its commencement. As they 

 are nearly all free animals, with power of rapid locomotion, 

 and with a relatively high development of their nervous 

 system and of their organs of sense, they are well adapted 

 by their instincts and their organs of animal life to admi- 

 nister to the vegetative, by distinguishing and overtaking 

 the most suitable and highly organized prey. As the sim- 

 ple and straight form is a character impressed upon the 

 alimentary canal of the articulata, both by the narrow 

 cylindrical form of the trunk and by their predaceous ha- 

 bits, we observe greater uniformity in its plan of structure 

 than in the other divisions of the animal kingdom, although 

 the endless modifications of their organs of relation enable 

 them to seek their prey in every element and in every situa- 

 tion. The mouth is here generally provided with masticating 



