218 University of California Publications in Zoology [Vol. 20 



undivided. The pairs of curved parabasals are especially prominent 

 and paired axostyles are evident, so that the cyst appears to have a 

 tangle of overlapping, stained strands from which the constituent 

 pairs of nuclei and their attendant neuromotor systems are dis- 

 entangled with increasing diiSculty as the divisions progress within 

 the as yet undivided cytoplasm. The increased size of the deeply stain- 

 ing parabasals, the curvature of the axostyles in the confinement of 

 the cyst, and the shifting of the nuclear pairs as mitosis proceeds, add 

 to the variety of relations presented in the successive stages of multiple 

 mitosis (pis. 25 and 26). 



The cysts are ellipsoidal bodies of hyaline, bluish, highly refractive 

 optical properties. They are quickly and easily discerned among the 

 faecal debris and are at once distinguished from all other cysts in the 

 faeces by their ellipsoidal form and the prominent parabasals and 

 axostyles which, in the fresh state, in Lugol's solution, in iodine-eosin, 

 and in iron haemotoxylin stains, stand out even more clearly than do 

 the nuclei. 



The shape of the cy.sts varies considerably in different races. 

 Figures on plates 25 and 26 were chosen to represent these variations 

 as well as those of a fluctuating nature. ' The most abundant race is 

 that represented in the ellipsoidal rather than spheroidal or elongated 

 cysts. These are symmetrically ellipsoidal, with the major axis 1.3 

 to 1.7 times the transverse in length. In some cysts (pi. 25, fig. 18) 

 the anterior end tapers slightly, giving an ovoidal form to the cyst, 

 thus reversing the proportions of the free stage. There is a stout race, 

 the free stage of which is as yet not studied, which has a cyst approach- 

 ing the spheroidal form with an axial ratio of 1 to 1.11 to 1.22 (pi. 25, 

 fig. 16 ; pi. 26, fig. 23 ) . This is not ba.sed on end views of ellipsoidal cysts. 



This stout race was found together with the ellipsoidal in one 

 instance of infection but it was the sole or predominant one in several 

 others, supporting the inference that this type of cyst may represent 

 a form-size race. The elongated type (pi. 25, fig. 21 ; pi. 26, fig. 24) is 

 probably not a form-race, but occurs in small numbers among the 

 ellipsoid cysts. In some instances in stained cysts the cytoplasm has 

 withdrawn locally from the cyst wall as though shrunken by artefact. 

 These lacunae also appear in some cysts in fresh smears as though the 

 cyst might under some circumstances contain more space than the 

 volume of the protoplasmic body. A few cysts (pi. 25, fig. 19; pi. 26, 

 fig. 30) are irregular in outline. 



The size of the cysts varies from 8.5 by 11.3 to 11 by 19,u. 

 Spheroidal races are 11.1 by 11.7 to 10.8 by 13.4/j,. 



