524 E. RAY LANKESTER. 



coeloinoccelous animals — the Appendiculata — is divided, the 

 other two being respectively the Cha?topoda and the Rotifera. 

 The Avord '^ Arthropoda " was first nsed in classification by 

 Siebold and Stannius (' Lehrbuch der vergleich. Auatomie,' 

 Berlin, 1845) as that of a primary division oE animals, the 

 others recognised in that treatise being Protozoa, Zoophyta, 

 Vermes, Mollusca, and Vertebrata. The names Condylopoda 

 and Gnathopoda have been subsequently proposed for the 

 same group. The word refers to the jointing of the chitinised 

 exo-skeleton of the limbs or lateral appendages of the animals 

 included, which are, roughly speaking, the Crustacea, Arach- 

 nida, Hexapoda (so-called ^' true insects"). Centipedes, and 

 Millipedes. This primary group was set up to indicate the 

 residuum of Cuvier's Articulata when his class Annelides 

 (the modern Chtetopoda) was removed from that " embranche- 

 ment." At the same time Siebold and Stannius renovated 

 the group Vermes of Linuasus, and placed in it the Chastopods 

 and the parasitic worms of Cuvier, besides the Rotifers and 

 Turbellarian worms. ^ 



' As a matter of fact the group Arthropoda itself, thus constituted, was 



precisely identical in its area with the class Insecta of Linnaeus, the Entonia 



of Aristotle. But by causes which it is not easy to trace the word "Insect" 



had become limited since the days of Linnaeus to the Hexapod Pterygote 



forms, to the exclusion of his Aptera. Lamarck's penetrating genius is chiefly 



responsible for the shrinkage of the word Lisecta, since it was lie who, forty 



years after Linnseus's death, set up and named the two great classes Crustacea 



and Arachnida (included by Linnaeus under Insecta as the order "Aptera") 



assigning to them equal rank with the remaining Insecta of Linnaeus, for 



which he proposed the very appropriate class-name " Hexapoda." Lamarck, 



however, appears not to have insisted on this name Hexapoda, and so the 



class of Pterygote Hexapods came to retain the group-name Insecta, which 



is, historically or etymologically, no more appropriate to them than it is to 



the classes Crustacea and Arachnida. The tendency to retain the original 



name of an old and coini)rehensive group for one of the fragments into which 



such group becomes divided by the advance of knowledge— instead of keeping 



the name for its logical use as a compreliensivc term, including the new 



divisions, each duly provided witii a new name — is most curiously illustrated 



in the history of the word Physiology. Cicero says, " Physiologia natura; 



ratio," and such was the meaning of the name Piiy siologus, given to a 



