34 



BIOLOGY OF THE PROTOZOA 



food requirements has undoubtedly been the cause of some form 

 changes as Biitschli has shown. Thus the proboscis-bearing species 

 and the asymmetrical Chilodon types may owe their characteristic 

 forms to such a shifting of the oral region (Fig. 13). 



The monaxonic types, while typically ellipsoidal in form, are 

 usually characterized by a spiral twisting of the cell body, espe- 

 cially in the rapidly moving forms. In some cases, notably in the 





•:^Z.<i 



P-i. 





rr 



Fig. 12. — Diphasic rhizopods. A, B, C, heliozoa-like and flagellated stages of 

 Dimorpha jnutans. (After Blochman.) D, E, F, Nagleria gruberi, amoeboid and 

 flagellated stages; E, origin of blepharoplast (bl) from endosome; r, rhizoplast. 

 (After C. W. Wilson.) 



flagellates Phacus lom/icauda , Phacus jryrum, Heferonema sp,, etc., 

 and in the ciliates M(iiiria, Paramecium, Mctopus sigmoidcs, etc., 

 the spiral twist is highly characteristic (Fig. 14), 



Bilateral symmetry is of rare occurrence among Protozoa; indeed 

 there seems to be only one really significant case, that of Giardia 

 (Fig. 15). Here the two nuclei, the motor complex, and the eight 

 flagella are arranged in the neatest bilateral manner. In some 



