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 succeeding 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 naturae. His classi- 

 ficatioD (1801-1812) is as follows : 

 Invertebrata. 



1. Apathetic Animals. 



Class I. INFUSORIA. 



Orders : Nuda, Appendiculata. 

 Class II. POLYPI. 



Orders : Ciliati (Rotifera), Denudati (Hydroids), Va- 

 ginati (Anthozoa and Polyzoa\ Natantes (Crinoids). 

 Class III. RADIARIA. 



Orders : Mollia (Acalephce), Echinoderma (including 



Actiniae). 

 Class IV. TUNICATA. 



Orders : Bothryllaria, Ascidia. 

 Class V. VERMES. 



Orders : Holies (Tape- Worms and Flukes), Rigiduli 

 (Nematoids), Hispiduli (Nais, etc.), Epizoarice 

 (Lernseans, etc.) 



2. Sensitive Animals. 



Class VI. INSECTA (Hexapoda). 



Orders: Aptera, Diptera, ffemiptera, Lepidoptera, 

 Hymenoptera, Neuroptera, Orthoptera, Coleoptera. 

 Class VII. ARACHNIDA. 



Orders: Antennato-Trachealia ( = Thysanura and 

 Myriapoda), Exantennato-Trachealia, Exantennato- 

 Branchialia. 

 Class VIII. CRUSTACEA. 



Orders : ffeterobranchia (Branchiopoda, Isopoda, Am- 

 phipoda, Stomapoda), Homobranchia (Decapoda). 



