8 AMOEBA LESS, 



times the chromatin is collected towards the surface or 

 periphery of the nucleus ; sometimes, again, it becomes 

 aggregated in the centre (g, h). One or more smaller 

 bodies, or nucleoli^ may also be present in the nucleus. 

 which is then distinguished as the nucleolus. 



When it is said that Amoebae sometimes have one kind of 

 nucleus and sometimes another, it must not be inferred that 

 the same animalcule varies in this respect. What is meant 

 is that there are found both in fresh and salt water many 

 kinds or species of Amoeba wiiich are distinguished from one 

 another, amongst other things, by the character of their 

 nuclei, just as the various species of Felis — the cat, lion, 

 tiger, lynx, &c. — are distinguished from one another, amongst 

 other things, by the colour and markings of their fur. 

 According to the method of binomial nomenclature intro- 

 duced into biology by Linnaeus, the same generic name 

 is applied to all such closely allied species, while each is 

 specially distinguished by a second or specific name of its 

 own. Thus under the ge7ius Amoeba are included Amoeba 

 proteus (Fig. I, c, E, and f), with long lobed pseudopods and 

 a nucleus containing evenly-disposed granules of chromatin; 

 A ^uar la (a and b), with short pseudopods and numerous 

 nuclei ; A. verrucosa (g and h) with crumpled or folded 

 surface, no well-marked pseudopods, and a nucleus with a 

 central aggregation of chromatin substance ; and many 

 others. 



Besides the nucleus, there is another structure frequently 

 visible in the living Amoeba. This is a clear, rounded space 

 in the protoplasm (c, E, and o, c. vac), which periodically 

 disappears with a sudden contraction and then slowly 

 reappears, its movements reminding one of the beating of a 

 minute colourless heart. It is called the contractile vacuole, 

 and consists of a cavity containing a watery fluid. 



