IX THE HISTORY AND SCOPE OF ZOOLOGY 325 



represent a series of steps in a scale of ascending com- 

 plexity, and it was thought possible thus to arrange 

 the animal kingdom in a single series, — the orders 

 within the classes succeedino; one another in regular 

 gradation, and the classes succeeding one another in a 

 similar rectilinear progression. Lamarck represents 

 most completely, both by his development theory (to 

 be further mentioned below) and by his scheme of 

 classification, the high-water mark of the popular but 

 fallacious conception of a scala natures. His classi- 

 fication (1801-1812) is as follows :— 

 Invertebrata. 



1. Apathetic Animals. 



Class I. Infusoria. 



Orders : Nuda^ Appendiculata. 

 Class 11. Polypi. 



Orders : Ciliati {Rotifer a), Bemidati (Hydroids), Ya- 

 ffinati {Anthozoa and Polyzoa), Natantes (Crinoids). 

 Class III. Radiaeia. 



Orders : Mollia {Acalephce), EcJmioderma (including 

 Actinice). 



Class IV. TUNICATA. 



Orders : Bothryllaria, Ascidia. 

 Class V. Vermes. 



Orders : Molles (Tape- Worms and Flukes), Rigididi 



(Nematoids), Hispididi (Nais, etc.), Epizoarim 



(Lernagans, etc.) 



2. Sensitive Animals. 



Class VI. Insect A {llexapoda). 



Orders : Aptera, Diptera^ Hemiptera^ Lepidoptera^ 

 Hymenojytera, Neuroptera, Orthoptera, Coleoptera. 

 Class VII. Arachnida. 



Orders: Antennato-Trachealia { = Thysanura and 

 Myriapoda), Exantennato-Trachealia,Exant€7inato- 

 Branchialia. 

 Class VIII. Crustacea. 



Orders : Heterohranchia {Branchiopoda^ Isopoda, Am- 

 phipoda, Stomapoda), Hoynohranchia {Decapoda). 



