AM(EBA. 89 



endure dryness for some time. In one grade (Gymnomyxa) 



the living matter is without any rind, and flows out in more 

 or less changeful threads and lobes, by the movements of which 

 the animals engulf their food and glide along. The others 

 (Corticata) have a definite rind, which in a large number 

 (Jnfusorians) bears motile cilia or flagella, but in the others 

 (Sporozod] is without any obvious locomotor structures. But 

 these three phases amoeboid, ciliate or flagellate, and en- 

 cysted may occur in the life history of one form ; and the 

 three main lines of evolution expressed in the old and still 

 useful threefold classification Rhizopods, Infusoria ns and 

 Gregarines is marked bv the predominant occurrence of the 

 amceboid, ciliate or flagellate, and encysted phase of cell life. 

 Many have a skeletal framework of lime, flint, or other 

 material, while within the cell there is a special kernel or 

 nucleus, or there mav be several. There are also other less 



/ * 



constant structures. A Protozoon multiplies by dividing into 

 two daughter units, or into a large number ; and two 

 individuals often unite, temporarily or permanently, in con- 

 jugation, which is analogous to the union of ovum and 

 spermatozoon in higher animals. A few types, instead of 

 remaining single cells, form by division or budding loose 

 colonies, taking a step, as it were, towards the Metazoa, but 

 never forming differentiated tissues. 



First Type of Protozoa AM<F.P,A. 



Ama'ba, a type of Rhizopods, especially of those in which 

 the outflowing processes of living matter (pseudopodid) are 

 blunt and finger-like (Lobosa). 



Description. Amceba proteus and some other species are 

 found in the mud of ponds ; A. terricola occurs in damp 

 earth. Some are just large enough to be seen with the 

 unaided eye. The diameter is often about one-hundredth 

 of an inch. Each is a unified corpuscle of living matter, 

 and glides over the surface of stone and plant by protruding 

 and retracting the pseudopodia. As they move the shape 

 constantly changes, whence the old (1755) name of " Proteus 

 animalcule/' Round the margin, which may show an 

 apparent radial striation, the cell substance is firmer and 

 clearer than it is in the interior, where it is more fluid, but 



