xxx.] CLASSIFICATION. 729 



be produced without the agency of living beings. Thus 

 the distinction between the organic and the inorganic 

 kingdoms seems to be breaking down, but our wonder at 

 the peculiar powers of carbon must increase at the same 

 time. 



In considering generalisation, the law of continuity was 

 applied chiefly to physical properties capable of mathe- 

 matical treatment. But in the classificatory sciences, also, 

 the same important principle is often beautifully ex- 

 emplified. Many objects or events seem to be entirely 

 exceptional and abnormal, and in regard to degree or 

 magnitude they may be so termed ; but it is often easy to 

 show that they are connected by intermediate links with 

 ordinary cases. In the organic kingdoms there is a common 

 groundwork of similarity running through all classes, 

 but particular actions and processes present themselves 

 conspicuously in particular families and classes. Tenacity 

 of life is most marked in the Eotifera, and some other 

 kinds of microscopic organisms, which can be dried and 

 boiled without loss of life. Beptiles are distinguished 

 by torpidity, and the length of time they can live without 

 food. Birds, on the contrary, exhibit ceaseless activity and 

 high muscular power. The ant is as conspicuous for 

 intelligence and size of brain among insects as the quad- 

 rumana and man among vertebrata. Among plants the 

 Leguminosse are distinguished by a tendency to sleep, 

 folding their leaves at the approach of night. In the 

 genus Mimosa, especially the Mimosa pudica, commonly 

 called the sensitive plant, the same tendency is magnified 

 into an extreme irritability, almost resembling voluntary 

 motion. More or less of the same irritability probably 

 belongs to vegetable forms of every kind, but it is of 

 course to be investigated with special ease in such an 

 extreme case. In the Gymnotus and Torpedo, we find that 

 organic structures can act like galvanic batteries. Are we 

 to suppose that such animals are entirely anomalous ex- 

 ceptions ; or may we not justly expect to find less intense 

 manifestations of electric action in all animals ? 



Some extraordinary differences between the modes of re- 

 production of animals have been shown to be far less than 

 was at first sight apparent. The lower animals seem to 

 differ entirely from the higher ones in the power of repro- 



