26 



THE GUIDE TO NATURE. 



colorless, and invisible to the naked eye, 

 yet they seem to achieve the purpose for 

 which they were created, whatever that 

 may be. They crawl over the ooze 

 of our ponds, they glide up the stems of 

 aquatic plants and hunt their prey among 

 the submerged leaves, and themselves 

 fall victims to other prowling creatures 

 higher in the scale of creation, or of the 

 naturalist's classification. Some havo- 

 been bandied back and forth between 

 the two sections, until the patient reade " 

 has begged for rest, and the lowly crea- 

 tures, if they could feel the blows di- 

 rected toward them, would long ago have 

 been annihilated by the concussions. 



One such, that in favorable circum- 

 stances may become visible to the unaid- 

 ed vision, is Volvos globaior, now be 

 lieved to be undoubtedly a plant, al- 

 though its experience with microscopists 

 must have caused the beautiful thing to 

 dissolve in laughter, if it could know 

 and feel. 



On those rare occasions, when Volvox 

 is visible to the naked eye, it is a charm- 

 ing object, although it is no more impres- 

 sive or imposing than a green globe ono 

 one-fiftieth of an inch in diameter. Yet 

 the little thing rises and floats and falls 

 through the water in graceful curves, 

 and long sweeps and sudden ascents tow- 

 ard the surface, constantly rolling lik; 

 the animated ball that it is, and by some 

 mysterious influence rarely colliding 

 with any of the innumerable company 

 of its fellows, which may fill the pond 

 until that is made green by its presence 

 It is to be found during the summei 

 months in almost all parts of the coun 

 try, but rarely in great numbers. The 

 writer has once only seen a small pond 

 so thickly habited by it, that the water 

 was tinted by its presence, and a spoon- 

 tul lifted out appeared to be moving 

 spontaneously, so numerous were the 

 Volvoxcs. Rut they have never since 

 appeared in that pool. They are tak- 

 en sparingly through the summer, and 

 have been captured from beneath ice four 

 inches thick. When Volvox was first 

 observed, the discoverer decided it to be 

 an animal, probably on account of its 

 freedom of movement, and its activity. 



When sufficiently magnified, the sur- 

 face of this delicate globe is everywhere 

 seen to be dotted with minute, green 



bodies that produce the faintly verdant 

 tinge that characterizes the plant, and 

 rather indirectly subserve the purposes 

 of locomotion. "These peripheral cells,' - 

 (I am quoting from Professor A. W. 

 Bennett) "contain each a green proto- 

 plasm-body, varying in shape according 

 to the age of the individual ; they usually 

 contain a minute starch granule, a red- 

 dish-brown 'eye-spot,' . . . and one 

 or two contractile vacuoles, . 

 They constitute a single peripheral layer 

 enveloping" the entire organism. 

 They have, however, as far as known 

 no reproductive function, and in th.i 

 respect stand almost alone among cells 

 endowed with a spontaneous power of 

 motion." 



It is these surface cells that bear tne 

 two, or more especially the one particular 

 body that lead investigating microscop- 

 ists to place Volvox among animals. 

 These are the vibratile cilia, by whos.; 

 action the globe advances and rotates, 

 and the contractile vacuole. None of 

 these organs is ever visible to the naked 

 eye. Even to see them with the micro- 

 scope demands a high magnifying power ; 

 to study them properly, calls for the best 

 and highest power lenses, careful illumi- 

 nation and the trained eye of a micro- 

 scopist. 



• The cilia are delicate, colorless 

 lashes that almost constantly beat the 

 water, and by their action urge the Vol- 

 vox along its graceful course. Two of 

 these vibratile lashes arise from each of 

 the peripheral cells, and in number have 

 been estimated to be about twenty- four 

 thousand. They are difficult to see, even 

 with favorable microscopical conditions. 

 It is only when they are quiet or at least 

 quiescent, that the exceedingly slender 

 threads can be demonstrated to exist. 



Each seems to be nothing but a deli- 

 cate, colorless filament, yet they vibrate 

 slowly or rapidly at the volition of the 

 Volvox ; the movement may cease ; it 

 may be resumed. How are these ac- 

 tions accomplished? Are these vibra- 

 tile appendages formed from threads of 

 vegetable muscle (if I may be pardoned 

 for so incorrect an expression as vege- 

 table muscle), that they contract and 

 relax at the will of their bearer? Is 

 Volvox, after all, an animal with muscu- 

 lar filaments studding its surface? If it 



