COLONIES OF ANIMALCULES. 



719 



countless living cells arranged into organs, each with its own special function 

 to perform for the life of the whole. Single cells multiply in several ways, 

 the simplest being that of the Amceba, which, creeping along the ground, 

 parts into two daughter Amoeb.ie, each of which creeps on its separate way. 

 In the case of free-swimming cells, like the Flagellata, separation into two 

 might not be so easy, especially if the mechanism of locomotion is not very 

 powerful as compared with the size of the body. In such creatures the cells, 

 though actually dividing, need not finally separate, but may swim about in 

 contact with one another ; and, if successive generations of cells thus remain 

 together, simple colonies arise. Several balls made up of flagellate cells 

 are known, in which all the whips of the component cells are turned 

 outward, and, by their movement, send the whole colony rolling along 

 through the water. The best known of these is Volvox (jlobator, which, on 

 account of the. bright green colour in its cells, is often claimed as a plant. 



It is clear again that colonies may also arise by the dividing up of cells 

 which are stationary. The daughter cells in this case may either grow up 

 simply alongside of the parent, or may 

 branch out from it. We are, however, 

 fairly safe in assuming that all the higher 

 animals arose from free- swimming, and 

 not from stationary colonies, a stationary 

 manner of life being but little conducive 

 to progress. In Fig. 7, A, we see 

 stationary colonies of Flagellata which, 

 but for the stalk of attachment, some- 

 what resemble Volvox above mentioned. 

 Another stationary colony is seen in the 

 same figure (B), and is formed by the 

 contiguous tubular sheaths of a number 

 of flagellate cells, each provided with 

 two whips. This colony forms folded, 

 fan-like growths, the height of the 

 whole structure being often not more 

 than t'j of an inch. Collared Flagel- 

 lates also form colonies, sometimes 

 being grouped together in flower-like 

 bunches on stalks, as in Fig. 7, C, or 

 floating about freely with the collars and whips projecting from a mass of 

 common protoplasm. A colony of this latter sort has been named Protos- 

 pongia, as it seems to foreshadow the arrangement of somewhat similar 

 collared cells found in the Sponges. 



Returning, however, to the Flagellata which remain single, i.e., do not 

 form colonies, reproduction takes place among them in several different 

 ways. Some Flagellata simply break up into parts, like the Ama?ba, others 

 detach only small pieces of their bodies, each piece developing into a new 

 animal, a process which is called budding or gemmation ; others, again, 

 reproduce themselves by a kind of internal budding called spore-formation. 

 The whole inside of the animal divides into a great number of nnnute 

 "spores," each of which, after resting a while, grows into an animal like 

 the paront. The Noctiluca (Fig. 6, C), for instance, which causes the 

 marine phosphorescence already alluded to, may pass through a resting stage 

 when it loses its whip and looks like a mere gelatinous ball (it is then said 



Fig^ 7.— Flagellate Colonies. 



A, Anthrophysa. 



B, Rhipidodendron. 



C, Codosigft. 



