IX THE HISTORY AND SCOPE OF ZOOLOGY 337 



tion of the entire structure of each animal, but on the 

 variations of a single organ, or on the really non- 

 significant fact of the structure of the egg. All such 

 single-fact systems have proved to be useless, and in 

 fact departures from the true line of growth of the 

 zoological system which was shaping itself year by 

 year unknown to those who so shaped it as a 

 genealogical tree. They were attempts to arrive at a 

 true knowledge of the relationships of animals by 

 " royal roads " ; their followers were landed in barren 

 wastes. 



R. Leuckart's * classification is as follows : 



Type 1. Coelenterata. 



Class I. POLYPI. 



Orders : Antkozoa and Cylicozoa. 



II. ACALEPH^E. 



Orders : Discophorce and Ctenophorce. 

 Type 2. Echinodermata. 

 Class I. PELMATOZOA. 



Orders : Cystidea and Crinoidea. 

 II. ACTINOZOA. 



Orders : EcMnida and Asterida. 



III. SCYTODEKMATA. 



Orders : Holothurice and Sipunculida. 



Type 3. Vermes. 



Class I. ANENTEE^ETI. 



Orders : Cestodes and Acanthocephali. 



1 Die Morphologie und die Verwandtschaftsverhaltnisse der ivirbellosen 

 Thiere, Brunswick, 1848. The Protozoa, recognised as a primary group 

 by Siebold and Stannius (Lehrbuch d. vergleich. Anatomie, Berlin, 1845), 

 are not included at all by Leuckart in his scheme. The name Protozoa 

 was first used by Goldfuss (1809) to include microscopic animals and 

 also the Polyps and Medusce, whilst Siebold and Stannius first used it in 

 its modern signification as comprising and limited to the Infusoria and 

 Rhizopoda. 



Z 



