PRINCIPAL SYSTEMS OF ZOOLOGY 237 



1st Grade. Intestinal Animals; also called Body-animals and Touc/j-animals. Only one 

 cavity; no head with a brain, only the lowest sense perfect, intestines and skin organs, 

 but no flesh, that is no bones, muscles, or nervous marrow = Invertebrata. 



Characterized by the development of the vegetative systems of organs, which are those 

 of digestion, circulation, and respiration. Hence — 



Cycle I. Digestive Animals. = Radiata. Essential character: no development beyond an 

 intestine. 

 Cl. 1 Infusoria. (Stomach animals). Mouth with cilia only, to vibrate. 

 Cl. 2. Polypi (Intestine animals). Mouth with lips and tentacles, to seize. 

 Cl. 3. Acalephae (Lacteal animals). Body traversed by tubes similar to the lymphatic 

 vessels. 



Cycle II. Circulalive Animals, zz: Mollusks. Essential character: intestine and vessels. 

 Cl. 4. Acephala (Biauriculate animals). Membranous heart with two auricles. 

 Cl. 5. Gasteropoda (Uniauriculate animals). Membranous heart with one auricle. 

 Cl. 6. Cephalopoda (Bicardial animals). Two hearts. 



Cycle III. Respirative ^nfma/5. = Articulata. Essential character: intestine, vessels, and 

 spiracles. 

 Cl. 7. Worms (Skin animals). Respire with the skin itself, or part of it, no articulated 



feet. 

 Cl. 8. Crustacea (Branchial animals). Gills or air tubes arising from the horny skin. 

 Cl. 9. Insects (Tracheal animals). Tracheae internally, gills externally as wings. 



2d Grade. Flesh Animals; also called Head-animals. = Vertebrata. Two cavities of the 

 body, surrounded by fleshy walls (bones and muscles) inclosing nervous marrow and 

 intestines. Head with brain; higher senses developed. Characterized by the develop- 

 ment of the animal systems, namely, the skeleton, the muscles, the nerves, and the 

 senses. 



Cycle IV. Carnal Animals proper. Senses not perfected. 



Cl. 10. Fishes (Bone-animals). Skeleton predominating, very much broken up; 



muscles white, brain without gyri, tongue without bone, nose not perforated, ear 



concealed, eyes without lids. 

 Cl. 11. Reptiles (Mw5c/e-animals). Muscles red, brain without convolutions, nose 



perforated, ear without external orifice, eyes immovable with imperfect lids. 

 Cl. 12. Birds (Nerve-dLniraals). Brain with convolutions, ears open, eyes immovable, 



lids imperfect. 



Cycle V. Se7isual Animals. All anatomical systems, and the senses perfected. 



Cl. 13. Mammalia (5en5e-animals). Tongue and nose fleshy, ears open, mostly with 

 a conch, eyes movable, with two distinct lids. 



The principles laid down by Oken, of which this classification is 

 the practical result for Zoology, may be summed up in the following 

 manner: The grades or great types of Animals are determined by 

 their anatomical systems, such as the body and head; or the intestines 

 and the flesh and senses. Hence two grades in the animal kingdom. 

 Animals are, as it were, the dismembered body of man made alive. 

 The classes of animals are the special representation in living forms 

 of the anatomical systems of the highest being in creation. 



Man is considered in this system not only as the key of the whole 



