16 INTRODUCTIOjST. 



IV. 



movement. But the sponges can scarcely be far removed from Fungia, nor can 

 that be separated from other corals : so that, though I am aware some naturalists 

 of eminence regard the sponges as vegetables, I cannot subscribe to that opinion, 

 but rather view them as exhibiting to us animal organization in its lowest con- 

 ceivable type, and parallel to vegetable organization, as that exists in the lowest 

 members of the class of Algas. 



This hasty glance at the animal kingdom teaches us that voluntary motion is a 

 character variable in degree, and at length reduced almost to zero within the 

 animal circle. On the other hand, we know that movements of a very extra- 

 ordinary character exist among the higher vegetables. Not merely the movement 

 of the fluids of plants within their cells, which has at least some analogy with the 

 motion of animal fluids ; but in such plants as the Sensitive-plant, the Venus's 

 Flytrap (Dioncea), and many others, movements of the limbs (shall I call them ?) as 

 singular as those of the Algse-spores, are sufficiently well known. And these move- 

 ments are affected by narcotics in a manner strikingly similar to the operation 

 of similar agents on the nervous system of animals. The common sensitive-plant, 

 indeed, only shrinks from the touch, but in the Desmodium gyrans a movement of 

 the leaves on their petioles is habitually kept up, as if the plant were fanning itself 

 continually. Such vegetable movements as these strike us by their rapidity, but 

 others of a like nature only escape us by their slowness. Thus the opening of the 

 leaves of many plants in sunlight and their closing regularly in the evening in 

 sleep ; the constant turning of the growing points towards the strongest light, and 

 other changes in position of various organs, are all vegetable movements which 

 would appear as voluntary as those of the Algse spores if they were equally rapid. 

 Their extreme slowness alone conceals their true nature. 



So then we find animals in which motion is reduced almost to a nullity ; and 

 vegetables as high in the scale as the Leguminosce exhibiting well marked move- 

 ments, facts which sufficiently establish the truth of our position that mere motion is 

 no proof of animality. But subtracting their movements from the Algfe-spores, 

 what other proof remains of their being animalcules ? None whatever. They do 

 not resemble animalcules either in their internal structure, their chemical compo- 

 sition, or their manner of feeding ; and their vegetable nature is sufficiently 

 marked by their decomposing carbonic acid, giving out oxygen in sunlight, and 

 containing starch. 



In the Vaucheria clavata, one of the species in which spores moved by cilia were 

 first observed, the spore is formed at the apices of the branches. The frond in 

 this plant is a cylindrical, branching cell, filled with a dense, green endochrome. A 

 portion of the contained endochrome immediately at the tips separates from that 

 which fills the remainder of the branch ; a dissepiment is formed, and that portion 

 cut off from the rest gradually consolidates into a spore, while the membranous 

 tube enlarges to admit of its growth. The young spore soon becomes elliptical, 

 and at length, being clothed with a skin and ready for emission, it escapes through 

 an opening then formed at the summit of the branch. The whole surface of the 

 spore, when emitted, is seen to be clothed with vibratile cilia whose vibrations 

 propel it through the water until it reaches a place suitable for germination. 



