30(1 Illinois State Laboratory of Natural History. 



pseudopodia also serve in obtaining food, for when they come 

 in contact with a diatom, for example, they flow around it 

 and entirely enclose it. Then the soft parts are digested, 

 and as the Amoeba moves along the undigested hard parts are 

 extruded. The structure of Difflugia is essentially the same 

 as that of Amoeba, with the exception that the Difflugia builds 

 for itself a small shell or lorica, using sand, diatoms, and 

 particles of other foreign matter. Arcella secretes a homo- 

 geneous chitinous shell, which is usually free from all foreign 

 substance. Euglypha secretes chitinous plates and then 

 unites them to form its shell. 



The subclass Heliozoa includes a number of the Sarcodina 

 characterized by having numerous thread-like pseudopodia. 

 These are not continuously thrust out and retracted, but have 

 a permanent form. The Radiolaria constitute another 

 subclass of the Sarcodina, but as it includes only marine 

 forms it is unnecessary to consider it here. The prevailing 

 mode of reproduction among the Sarcodina is division, 

 although budding and spore formation also occur. 



The class Sporozoa is composed of a number of Protozoa 

 which reproduce by means of spore formation. The occur- 

 rence of fission or budding among any members of the 

 group has not as yet been demonstrated. All of them are 

 parasitic, living in the intestines or in other organs or tissues 

 of higher animals, and therefore show a marked degeneration 

 of structure. Gregarina may be taken as a type. It is more 

 or less oval in outline, with the protoplasm differentiated 

 into a well-marked endoplasm and ectoplasm. The body is 

 constricted at about one third of its length from the anterior 

 end. A nucleus is present, but pseudopodia and the con- 

 tractile vacuole are wanting. 



In the class Mastigophora the members of the order Flagcl- 

 lata are characterized by the possession of one or more flagella 

 which serve as organs of locomotion, and also aid the animal 

 in securing food, since by means of them a constant current 

 of water is directed towards the mouth. The well-known 

 Euglena may be considered as a type. The body is elongate 

 and more or less cylindrical, and is highly flexible and very 



