28 PROCEEDINGS OP THE ACADEMY OF [1886. 



motion growing more sluggish as the defensive avmor grows 

 more efficient. But in the whole kingdom, motion persists as one 

 of the defensive agencies. No animal exists without some power 

 of motion, by whose aid it withdraws or otherwise escapes from 

 danger. 



In the plant kingdom, on the contrary, no defensive motion 

 exists. Mechanical defense exists alone. This does not apply to 

 those minute swimming organisms which lie near the root of the 

 plant and animal kingdoms. But in all the higher plants no 

 motion exists, so far as I am aware, that is useful as a protection. 

 Thus the possession of protective motions by all animals, and 

 the lack of them by all plants, serve as a point of distinction 

 between the two kingdoms. 



In regard to aggressive motions, this rule does not so fully 

 hold good. All animals have aggressive motions. Nearly all 

 plants are destitute of them. Yet a few plants possess them. We 

 have instances of aggressive motions in the case of the creeping 

 Fungi, and of the Insectivorous plants. Yet apart from these 

 cases, the plant kingdom seems devoid of motions useful either 

 for attack or. defense, and trusts wholly to mechanical appliances. 

 With the mechanical, however, must be included chemical appli- 

 ances, as in the case of poisonous or disagreeable juices. 



One more query remains. Wh}^, in the early days of the animal 

 kingdom, as known to us, was there such a marked tendency to 

 trust to mechanical defense, while in the later era the tendency 

 has been towards motion as the main protective agent ? If we 

 consider the early conditions of animal life, this is not difficult 

 to comprehend. There is every reason to believe that the various 

 organs of animals were very slowly evolved. In a former com- 

 munication I have advanced the h3qiothesis that the early animals 

 were for a long time naked forms, parti}', at least, through lack 

 of the evolution of glands necessary to produce hard coverings. 

 These early animals also moved by means of cilia only, if we can 

 trust the evidences from embryology, and from the lower existing 

 forms. The development of nerves and muscles was a very slow 

 process. The evolution of a form and of swimming organs giving 

 high efficiency to muscular action, was probabl}^ much slower. 

 The early animals possessed of muscles had probably a very 

 inefficient motor apparatus, and were very sluggish in their 

 movements. With the development of armor-producing power, 



