260 LEISURE-TIME STUDIES. 



are provided. And, perhaps, the most convincing proof of 

 the impossibility of distinguishing the animal from the plant, ' 

 not only as regards the possession of motor powers by the 

 latter, but also in respect of similarity in appearance, is 

 afforded by the case of the volvox, or " globe animalcule," 

 as it is termed, an organism familiar to every microscopist, 

 and met with in stagnant waters. A volvox (d) presents 

 the appearance of a hollow sphere, the edge of which 

 is formed of numerous little green bodies, each provided 

 with two long vibrating "tails." By means of the move- 

 ments of the latter organs, this living sphere rolls over 

 and over upon itself, and paddles its way amongst its 

 neighbours. When such beings are beheld, surrounded 

 by a crowd of true animalcules (e to /), the resemblance 

 between the two groups of forms is seen to be of very close 

 description. Volvox might, indeed, be very well classified 

 as an animalcule, if form and power of motion count for 

 anything in the framing of distinctions between animals and 

 plants. But that this organism is a true plant, is proved by 

 its mode of reproduction, and by many other traits of direct 

 correspondence with the alg?e; and there are many other 

 free-swimming organisms, the nature of which has been 

 similarly determined to be that of plants. The old group of 

 the "infusorian" animalcules, as at first constituted, and in 

 which volvox and its neighbours were contained, was a most 

 motley assemblage of beings of many different ranks and 

 grades, drawn from both animal and plant worlds; the 

 advance of microscopic inquiry resulting in the re-arrange- 

 ment of this heterogeneous group, and in its being literally 

 weeded out and its contents distributed far and wide in the 

 realms of living nature. 



Along with the distinctions derived from the power of 

 motion now no longer relied upon, but which the older 

 naturalists regarded as of stable kind, another means of 

 separating animals from plants was believed to exist in the 

 possession by animals of an internal sac or cavity, repre- 

 sented in its fullest development by the digestive system of 



