THE MICROSCOPE AS A RECREATION 131 



can be imagined, but it fulfils all the necessary functions, and, 

 moreover, the constant introduction of water into different parts 

 of the jelly tends to supply the necessary oxygen to keep the 

 animal healthy. 



This Contractile Vacuole, as the bubble is named, is the earliest 

 germ of both a digestive and a respiratory system, and we shall 

 now see how from this simple commencement a gradual growth 

 in complexity can be traced. 



The bubble of the Amoeba forms at any convenient position 

 within its substance, and in some of the Protozoa several of such 

 bubbles form ; but the second development is to be found in those 

 allied creatures in which the bubble is always in the same place 

 in the same species, and the water drains from the rest of the body 

 to that spot. 



In the next stage the bubble is no longer a perfect sphere, 

 but has one or more extensions, until in the final stage there are 

 minute channels all over the creature which communicate with 

 the main bubble, thus creating a complex drainage system, and 

 this is as far as digestion is developed in the Protozoa. 



The development of a mouth presents features of equal 

 interest. 



The Amoeba has no mouth — it does not eat, it engulfs. 



The Difflugia is similar, but its area of action is reduced by 

 the fact that a large portion of its body is enclosed in a shell. 



The Heliozoa also have no special feeding organ. When an 

 object becomes entangled in their fine filaments of jelly, it may, 

 if very small, find its way for digestion into the interior of the 

 shell, but as likely as not the fine rays may join up around the 

 object outside the main body, and digestion will proceed 

 there just as weU as in the interior. 



There is another series of animals called the Acineta, which 

 somewhat resemble the Heliozoa in that they are provided with 

 long, ray-like projections which are hard 

 or leathery except at the tips. Here they 

 swell out into small knobs of soft material, 

 through which small portions of food can 

 be taken in. Such organisms may be con- 

 sidered as having hundreds of mouths. 



Another series shows a much more 

 direct development. On these the skin is 

 hard except in patches, where alone food 

 can enter; and around these soft patches Fig. 127.— Acineta. 

 there is usually a ring of rapidly vibra- 

 ting hairs, which create a current, bringing the floating 

 particles into contact with the absorbent portion or portions of 

 the body. The Vorticellse (Fig. 124) have a disc-shaped ab- 

 sorbent surface surrounded by the strong ring of vibrating hairs 



The Stentor (Fig. 125), which is larger and a most voracioua 



