PRINCIPAL SYSTEMS OF ZOOLOGY 



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II. Sensitive Animals. 

 Cl. 6. Insects. (Hexapods.) Ord. Aptera, Diptera, Hem- 



iptera, Lcpidoptera, Hymenoptera, Neuroptera, 



Orthoptera, Coleoptera. 

 Cl. 7. Arachnids. Ord. Antennato-tracheales (Thysanura 



and Myriapoda), Exantennato-tracheales and Ex- 



antennato-branchiales (Arachnids proper.) 

 Cl. 8. Crustacea. Ord. Heterobranchia (Branchipoda, 



Isopoda, Amphipoda, Stomapoda) and Homo- 



branchia (Decapoda.) 

 Cl. 9. Annelids. Ord. Apoda, Antennata, Sedentaria. 

 Cl. 10. Cirripeds. Ord. Scssilia and Pedunculata. 

 Cl. 11. Conchifcra. Ord. Dimyaria, Monomyaria. 

 Cl. 12. MoUusks. Ord. Pteropoda, Gasteropoda, Tracheli- 



poda, Cephalopoda, Heteropoda. 



Feel, but obtain from 

 their sensations only per- 

 ceptions of objects, a sort 

 of simple ideas, which they 

 are unable to combine to 

 obtain complex ones. No 

 vertebral column; a brain 

 and mostly an elongated 

 medullary mass; some dis- 

 tinct senses; muscles at- 

 tached under the skin; 

 form symmetrical, the 

 parts being in pairs. 



III. Intelligent Animals. 



Cl. 13. Fishes. 

 Cl. 14. Reptiles. 

 Cl. 15. Birds. 

 Cl. 16. Mammalia. 



VERTEBRATA. 



Feel; acquire preservable ideas; perform with 

 them operations by which they obtain others; are 

 intelligent in different degrees. A vertebral column; 

 * a brain and a spinal marrow; distinct senses; the 

 muscles attached to the internal skeleton; form 

 symmetrical, the parts being in pairs. 



It is not easy to appreciate correctly the system of Lamarck, as it 

 combines abstract conceptions with structural considerations and an 

 artificial endeavor to arrange all animals in continuous series. The 

 primary subdivision of the animal kingdom into Invertebrata and 

 Vertebra ta corresponds, as I have stated above, to that of Anaima and 

 Enaima of Aristotle. The three leading groups designated under the 

 name of Apathetic, Sensitive, and Intelligent animals, are an imita- 

 tion of the four branches of Cuvier; but far from resting upon such 

 a definite idea as the divisions of Cuvier, which involve a special plan 

 of structure, they are founded upon the assumption that the psychical 

 faculties of animals present a serial gradation, which, when applied 

 as a principle of cla,ssification, is certainly not admissible. To say that 

 neither Infusoria, nor Polypi, nor Radiata, nor Tunicata, nor Worms 

 feel is certainly a very erroneous assertion. They manifest sensations 

 quite as distinctly as many of the animals included in the second 

 type which are called Sensitive. And as to the other assertion, that 

 they move only by their excited irritability, we need only watch the 

 Starfishes to be satisfied that their motions are determined by internal 

 impulses and not by external excitation. Modern investigations have 

 shown that most of them have a nervous system, and many even or- 

 gans of senses. 



