278 



CHAPTERS ON EVOLUTION. 



are to be regarded as exhibiting a compound constitution. For, in 

 these animalcules, which are as a rule of compound nature (Fig. 185, 

 b\ the growth of new divisions of the shell takes place by a process 

 of budding, and through the production of new protoplasmic units 

 which remain organically connected with the original mass. Nor 

 are the lowest plants to be left out of consideration in this recital 

 of primitive colony-making. The cryptogamic botanist well knows 

 certain green specks of microscopic size, each called Chlamydomonas, 

 which swim freely in fresh waters, by means of two long cilia, or 

 miniature eye-lashes, projecting from one extremity of the body. 

 Now, there exist in stagnant waters certain other curious bodies, 

 long known as "Globe-animalcules," before they were ascertained 

 to be lower plants. Each of these bodies is scientifically named a 

 Volvox (Fig. 1 86, d), and appears to consist of a hollow globe or 

 sphere, covered with innumerable little specks of bright green, and 



FIG. 186. VOLVOX (<) AND VARIOUS ANIMALCULES. 



swimming freely through the water by the waving action of the fine 

 cilia which fringe its body. More minutely examined, this rolling 

 globe is found to consist of a collection of little green bodies, 

 each of which, in all essential details, exactly resembles a single 

 Chlamydomonas. The filaments fringing the volvox are in reality 

 pairs of cilia like those of Chlamydomonas, and are attached to 

 the little green bodies aforesaid. Thus volvox, so far from being 

 an animal, is, firstly, a rootless lower plant; and, secondly, so far 

 from being one plant, volvox is in reality a colony of the lowest 

 members of the vegetable world. There are many other Alga (or 

 lowest plants) which resemble volvox in their compound nature ; and 

 thus the beginnings of plant-life appear to present us with a ten- 

 dency towards colonisation, similar to that which faces us on the 

 threshold of the other series of living beings. 



In the curious group of the sponges (Fig. 187), we may find our next 



