IV. INTRODUCTION. 15 



In some Algas a movement from place to place continues through the life of the 

 individual, while in others, as in the zoospores of which I have just spoken, it is 

 confined to a short period, often to a few hours, in the transition state of 

 the spore, after it escapes fi-om the parent filament and until it fixes itself 

 and germinates. Many observers have recorded these observations, which are to 

 be found detailed in various periodicals.* I shall here notice onl}^ a few cases illus- 

 trative of the various kinds of movement. The most ordinary of these movements 

 is effected by means of vibratile cilia or hairs, produced by the membrane of the 

 spore, and which by rapid backward and forward motion, like that of so many 

 microscopic oars, propel the body through the water in dififerent directions, accord- 

 ing as the movement is most directed to one side or the other. Sometimes the little 

 spores, under the influence of these cilia, are seen to spin round and round in widen- 

 ing circles ; but at other times change of direction, pauses, accelerations, &c. take 

 place during the voyage, which look almost like voluntary alterations, or as if the 

 spore were guided by a principle of the nature of animal will. Hence many 

 observers do not hesitate to call these moving spores animalcules^ and to consider 

 them of the same nature as the simpler infusorial animals. 



This, as it appears to me, is a conclusion which ought not to be hastily assumed, 

 not merely taking into consideration the extremely minute size of the little bodies 

 to be examined, and the consequent danger of our being deceived as to the cause 

 of movement, and of its interruption and resumption, but also remembering the facts 

 ascertained by Mr. Brown, of the movement of small particles of all mineral sub- 

 stances which he examined. Many of the spores in question are sufficiently small 

 to come under the Brownian law, though others are of larger size. Besides, if we 

 regard the moving spores as animalcules, we must either adopt the paradox that a 

 vegetable produces an animal, which is then changed into a vegetable, and the process 

 repeated through successive generations, every one of these vegetables having been 

 animal in its infancy ; or else, notwithstanding their strongly marked vegetable cha- 

 racteristics, we must remove to the animal kingdom all Algaa with moving spores. 



Neither of these violent measures is necessary, if we admit that mere motion, 

 apart from other characters, is no proof of animality. Though motion under the 

 control of a will be indeed one of the charter privileges of the higher animals, we see 

 it gradually reduced as we descend in the animal scale, until at last it is nearly lost 

 altogether. Long before we reach the lowest circles in the animal world, we 

 meet with animals which are fixed through the greater part of their lives to the rocks 

 on which they grow, and some of them have scarcely any obvious movement on their 

 point of attachment. In some the surface, like that of the Algae-spores, is clothed 

 with cilia which drive floating particles of food within reach of the mouth; in others 

 even these rudimentary prehensile organs are dispensed with, and the animal exists 

 as a scarcely irritable flesh expanded on a framework. This would seem to be the 

 case in the corals of the genus Fungia, if the accounts given of those animals be 

 correct ; while in the sponges the animal structure and organization are still further 

 reduced, so as almost to contravene our preconceived notions of animal-will and 



• See Annales des Sciences Natardles ; Taylor^s Ann. Nat. Hist. ; the Linncea, ^-c. various volumes. 



