spores, and their cysts or spores, since the metabolic processes 

 are in abeyance and there is no necessity for interchange 

 between the cytoplasm and the surrounding medium, are 

 enclosed within a thick resistent casing resembling in formation 

 and in composition the lignitic investment of the woody cells 

 of plants. 



It is of interest to note that in the higher animals organic 

 skeletons are always external, as in the crustaceans, tunicates, 

 insects, etc., bearing the same relation to the body of the 

 animal as a whole that the woody portion of a plant cell does 

 to the rest of the cell, or if internal, as a vertebrate notochord, 

 they are modified by the development of vacuoles and cuticular 

 structures into a form resembling the vegetable parench3ai'ia of 

 plants ; while inorganic skeletons, found in the vertebrates, are 

 internal and bear somewhat the same relation to the body as a 

 whole that the raphides of plants or the skeletal structures of 

 the myxomycètes or radiolarians do to the cells which contain 

 them. 



The Protozoa may be defined as organisms which are mostly 

 solitary, rounded, ovoid or somewhat elongated, never (excep- 

 ting for a few parasitic types which live under plant conditions) 

 filiform ; in the few colonial cypesthe individ uals are irregularly 

 massed or more or less radially grouped ; if continuous cells are 

 formed the arrangement of these is spiral, in two or more alter- 

 nating rows, or irregular, very exceptionally in a continous 

 row ; chains are very rare, and are formed by the adherence of 

 a number of similar individuals. The Thallophyta are not usually 

 solitary, and if so are predominently elongated or filiform, the 

 simpler types usuall}^ forming chains or films and the higher, 

 by linear and subsequently ramifying growth from the original 

 germ cell, a more or less complicated thallus. 



The simple animal, feeding only upon organic substances 

 which, though with a high food value, are relatively rare and 

 soon exhausted in any given locality, and not dependent upon 

 light for the transformation of its food into organic form, finds 

 the most advantage in a rounded or radiate body capable of 

 reaching out in any direction, and in a compact motile body 

 enabling it to search for food. 



The simple plant, on the other hand, finds its food much 

 more generally distributed, one place being as well supplied 



