I.] ANIMALS AND PLANTS CONTRASTED. 15 



power of locomotion, and it is easy to see that the rotate 

 or centrifugal construction would place the organism at 

 a comparative disadvantage, because its seat of sensation 

 is farthest removed from the external stimuli. But the 

 worm- like organisms "being longitudinal and bilat- 

 eral," writes Cope, "one extremity becomes differen- 

 tiated by first contact with the environment." In other 

 words, the animal type has shown a cephalic, or head- 

 forming, evolution in consequence of the bilateralism of 

 structure. The individual has become concentrated. 

 Out of this worm -form type, therefore, all the higher 

 ranges of zootypic evolution have sprung, and one is al- 

 most tempted to read a literal truth into David's lamen- 

 tation that " I am a worm, and no man." 



If, now, we turn to plants, we find the rotate or peri- 

 pheral arrangement of parts emphasized in all the higher 

 ranges of forms. The most marked bilateralism in the 

 plant Avorld is amongst the bacteria, desmids, and the 

 like, in which locomotion is markedly developed; and 

 these are also amongst the lowest plant -types. But 

 plants soon become attacihed to the earth, or, as Cope 

 terais them, they are "earth -parasites." They therefore 

 found it to their advantage to reach out in every direc- 

 tion from their support in the search for food. Whilst 

 the centrifugal arrangement has strongly tended to dis- 

 appear in the animal creation, it has tended with equal 

 strength to persist and to augment itself in the plant 

 creation. Its marked development amongst plants be- 

 gan with the acquirement of terrestrial life, and with the 

 consequent evolution of the asexual or sporophytic type 

 of vegetation. Normally, the higher type of plant bears 

 its parts more or less equally upon all sides, and the 

 limit t*^ errowth is still determined by the immediate en- 



