94 STUDIES IN ANIMAL LIFE. 



er cause. What is this cause ? Mr. Darwin holds 

 that "propinquity of descent the only known 

 cause of the similarity of organic beings is the 

 bond, hidden as it is by various degrees of modifi- 

 cation, which is partially revealed to us by our 

 classifications"* " that the characters which natu- 

 ralists consider as showing true affinity between 

 any two or more species are those which have been 

 inherited from a common parent, and in so far all 

 true classification is genealogical; that community 

 of descent is the hidden bond which naturalists 

 have been unconsciously seeking, and not some 

 unknown plan of creation, or the enunciation of 

 general propositions, and the mere putting together 

 and separating objects more or less alike."f 



Before proceeding to open the philosophical dis- 

 cussion which inevitably arises on the mention of 

 Mr. Darwin's book, I will here set down the chief 

 groups, according to Cuvier's classification, for the 

 benefit of the tyro in natural history, who will easi- 

 ly remember them, and will find the knowledge 

 constantly invoked. 



There are four sub-kingdoms, or branches : 1. 

 Vertebrata; 2. Mollusca; 3. Articulata; 4. Eadi- 

 ata. 



The VERTEBRATA consist of four classes : Mam- 

 malia, Birds, Eeptiles, and Fishes. 



The MOLLUSCA consist of six classes: Cephalo- 

 poda (cuttlefish), Pteropoda, Gasteropoda (snails, 



* DARWIN : Origin of Species, p. 414. t Ibid., p. 420. 



