208 HANDBOOK OF PROTOZOOLOGY 



teristically discoidal. But various modifications in nuclear 

 forms are equally characteristic of the species. Food vacuoles 

 contain numerous organisms co-existing in the water. Crystals 

 are elongated bipyramid and measure up to 4.5 microns in 

 length (Schaeffer). The development is not well established. 

 Asexual reproduction is usually binary fission, but under cer- 

 tain conditions division into four individuals is said to be of 

 common occurrence (Doflein). Encystment is common. By 

 using this amoeba Gruber found the now well-established fact 

 that'"the nucleus and cytoplasm are dependent upon each other. 



Amoeba discoides Schaeffer (Fig. 80, e-g). Body about 400 

 microns long during movement. A few blunt and smooth 

 lobopodia. Endoplasm contains bipyramidal truncate crystals, 

 about 2.5 microns in length. The nucleus is always discoidal in 

 form, without infolded surface. Usually one contractile vacuole. 

 In fresh water. 



Amoeba dubia Schaeffer (Fig. 80, h-j). Body about 400 

 microns in diameter. Numerous pseudopodia flattened and 

 with smooth surface. The nucleus circular in front view, oblong 

 in profile. Crystals few in number, but large and of various 

 shape. Contractile vacuole one or more. In fresh water. 



Amoeba verrucosa Ehrenberg (Fig. 81, a, b). Body irregu- 

 larly rounded with wart-like expansions. Body surface is 

 usually wrinkled, as though invested with a membrane. The 

 diameter varies from 50 to 200 microns. Pseudopodia short, 

 broad, and blunt. Differentiation of the cytoplasm is fairly 

 distinct. The nucleus is ovoidal. The contractile vacuole is soli- 

 tary and large. Multiplication by binary fission. Fresh water 

 among algae. 



Genus Pelomyxa Greeff. A large sluggish amoeba which 

 contains a few to numerous nuclei. The cytoplasmic differentia- 

 tion is poor. Pseudopodia small in number and are short and 

 broad; the animal undergoing a rolling movement. Besides the 

 nuclei, diatoms, bacteria, water vacuoles and sand-grains, endo- 

 plasm usually contains refractile bodies which are thought to be 

 either reserve food material similar to glycogen or metabolic 

 products used by symbiotic bacteria. Contractile vacuole has 

 not been noticed with certainty. Multiplication by binary fis- 

 sion. Gamete formation has been reported; it is presumed that 



