VOLVOCINBiE. 259 



histoiy of the species before us ; since it does not include the 

 performance of any true Generative act. There can be little 

 doubt that, in some stage of its existence, a " conjugation" of two 

 cells occurs, as in the preceding case ; and the attention of ob- 

 servers should be directed to its discovery, as vp^ell as to the de- 

 tection of other varieties in the condition of this interesting little 

 Plant, which will be probably found to present themselves before 

 and after the performance of that act. 



157. From the composite motile foi'ms of the preceding type, 

 the transition is easy to the group of Vol- 

 vocinece, — an assemblage of minute Plants t^"»- ^9 



of the greatest interest to the Microscopist, 

 on account both of the Animalcule-like 

 activity of their movements, and of the 



freat beauty and regularity of their forms, 

 'he most remarkable example of this group, 

 is the well-known Volvox glohator (Fig. 69), 

 or "globe-animalcule;" which is not un- 

 common in fresh-water pools, and which, 

 attaining a diameter of l-30th of an inch, 

 may be seen with the naked eye, when the 

 drop containing it is held up to the light, voWox cibbaior. 



swimming through the water which it in- 

 habits. Its onward motion is usually of a rolling kind ; but it 

 sometimes slides smoothly along, without turning on its axis ; 

 whilst sometimes, again, it rotates like a top, without changing 

 its position. When examined with a sufficient magnifying 

 power, the Volvox is seen to consist of a hollow sphere, com- 

 posed of a very pellucid material, which is studded at regular 

 intervals with minute green spots, and which is often (but not 

 constantly) traversed by green threads connecting these spots to- 

 gether. From each of the spots proceed two long cilia ; so that 

 the entire surface is beset with these vibratile filaments, to whose 

 combined action its movements are due. Within the external 

 sphere, there maj' generally be seen from two to twenty other 

 globes, of a darker color, and of varying sizes ; the smaller of 

 these are attached to the inner surface of the investing sphere, 

 and project into its cavity ; but the larger lie freely within the 

 cavity, and may often be observed to revolve by the agency of 

 their own ciliary filaments. After a time, the original sphere 

 bursts, the contained sphericles swim forth and speedily develope 

 themselves into the likeness of that within which they have been 

 evolved ; their component particles, which are at first closely 

 aggregated together, being separated from each other by the in- 

 terposition of the transparent pellicle. It was long supposed 

 that the Volvox was a single Animal; and it was first shown to 

 be a composite fabric, made up of a repetition of organisms in 

 all respects similar to each other, by Prof. Ehrenberg ; -who, 

 however, considered these organisms as Monads, and described 



