82 



duct, which is double in the elephant, usually opens separately into 

 the duodenum. 



RECAPITULATION. 



1. A digestive cavity is the most universal organ in animals, and 

 exists in all, with the exception of some of the monads. 



2. Masticating, salivary, and biliary organs are found in the 

 higher radiata. 



3. All these parts are more highly developed in the articulata, 

 and one or two gall-bladders are present. 



4. There has been no gall-bladder found in the mollusca. 



5. The stomach receives the biliary and pancreatic fluids in all 

 the invertebrata. 



6. The invertebrated animals possess no portal circulation. 



7. In the vertebrate the alimentary canal always swells out into 

 a gastric enlargement. The tributary organs are large and conglo- 

 merate, and the salivary glands are rarely absent. 



8. The duodenum receives the biliary and pancreatic secretions, 

 and there are no teeth found in the stomach. 



9. As a general rule the alimentary canal is larger and longer in 

 the vegetable-eating animals, than in those that live on flesh. 



10. Fishes have a simple form of alimentary canal, their teeth are 

 often numerous, as in the pike, rarely absent as in the sturgeon, 

 their salivary glands are rudimental, or entirely wanting, and their 

 whole canal often measures but half the length of the body. 



11. The digestive apparatus undergoes interesting changes during 

 the metamorphosis of the frog, &c. 



12. The teeth are absent in birds, and their place supplied by bill 

 and gizzard. 



13. The crop is double in the pigeon, single in the fowl, and 

 absent from the goose. The gizzard is thick and powerful in the 

 granivorous, but thin and membranous in the carnivorous species, 

 and the great intestine terminates in the dilatable rectal vestibule 

 which receives the openings of the ureters, of the oviducts, or vasa 

 deferentia, and of the Bursa Fabricii. 



14. The teeth are greatly modified in the mammalia, being 

 rarely absent, as in the man is or pangolin, the myrmecophaga and 

 the echidna. 



15. The digestive system is most complex in the herbivorous 

 ruminantia, and most simple in the carnivora ; in the latter the 

 food requires but little elaboration, hence the form of the teeth, and 

 the great strength of the jaws are admirably adapted for seizing and 

 tearing their living prey, here also we have a simple stomach, and 

 a short intestine, without any provision to retard its contents. In 

 the ruminantia, on the contrary, the jaws are elongated, and admit 

 of free lateral motion with flat grinding teeth, the stomach is com- 

 plicated, and the intestine long and sacculated ; in fact all things 



