54 THE DATA OF BIOLOGY. 



cially of tlie lower orders, are able to move their external 

 parts in relation to each other, and also to move about from 

 place to place. Illustrations in abundance will occur to all 

 students of recent Natural History — such illustrations as the 

 active locomotion of the zoospores of many Algae, the rhyth- 

 mical bondings of the Oscillatorioe^ the rambling progression 

 of the DiatomacecB. In fact many of these smallest vegetals, 

 and many of the larger ones in their early stages, display a 

 mechanical activity not distinguishable from that of the 

 simplest animals. Among w^ell-organized plants, which are 

 never locomotive in their adult states, we still not unfre- 

 quently meet with relative motions of parts. To such fami- 

 liar cases as those of the Sensitive plant and the Yenus' 

 fly-trap, many others may be added. When its base is 

 irritated, the stamen of the Berberry flower leans over and 

 touches the pistil. If the stamens of the common wild Cistus 

 be gently brushed with the finger, they spread themselves — 

 bending away from the seed-vessel. And some of the orchid- 

 flowers, as Mr. Darwin has recently shown, shoot out masses 

 of pollen on to the entering bee, when its trunk is thrust 

 down in search of honey. 



Though the power of moving is not, as we see, a character- 

 istic of animals alone, yet in them, considered as a class, it is 

 manifested to an extent so marked, as practically to become 

 one of their distinctive characters — indeed, we may say, their 

 most distinctive character. For it is by their immensely 

 greater ability to generate mechanical motion, that animals 

 are enabled to perform those actions which constitute their 

 visible lives; and it is by their immensely greater ability to 

 generate mechanical motion, that the higher orders of animals 

 are most obviously distinguished from the lower orders. 

 Though, on remembering the seemingly active movements of 

 infusoria, some will perhaps question this last-named con- 

 trast ; yet, on comparing the quantities of matter propelled 

 through given spaces in given times, they will see that the 

 momentum evolved is far less in the protozoa than in the 



