34 University of California PiiblicatioHs i)i Zoology [Vol. 16 



in life a crystal-clear vesicle on the outer ends of the epithelial cells. 

 The posterior end tapers down abruptly to a short, very mobile tail 

 having in it the tip of the axostyle. Its mobility is indicated by its 

 various positions in our figures (pi. 5, figs. 3, 5, 11). 



This organism is one of the so-called diplozoic flagellates consisting 

 of two unparted cells in a condition such as might occur if mitosis 

 of a unicellular flagellate with accompanying division of all cell 

 organelles except the axostyle should take place without subsequent 

 plasmotomy. It is in reality a binucleate somatella with all organelles 

 in duplicate (except the axostyle and cytostome), but with these 

 organelles in a bilateral arrangement about a single axostyle. The 

 cytoplasm shows no duplicity of external form. It is one individual, 

 not a colony of similar cells, nor two incompletely divided ones, but 

 two mutually interadapted cells forming a bilaterally symmetrical 

 organism. 



The organelles (fig. A) of this simplest (from the standpoint of 

 numbers only) possible multicellular organism consist of two nuclei 

 («MC.), two blepharoplasts (bleph.) from both of which arises one 

 interconnecting neuromotor sj'stem joining all of the organelles, one 

 axostyle {ax.), two paraba-sal bodies (par. b.), and one large ventral 

 cup or cytostome icyt.). 



The two nuclei {nuc.) are ellipsoidal bodies, with distinct nuclear 

 membranes, subcentral karoyosomes, sometimes with surrounding halo, 

 and remarkably little chromatin as a rule outside of the karyosome. 

 They are about 4 by 2.5 /n in length and transverse diameter respec- 

 tively, and lie near the ventral surface, .synunetrically placed near 

 the middle of the cytoplasmic mass, with their long axis diverging 

 5°-20° posteriorly from the main axis of the organism. From the 

 Karyosome of each a rhizoplast (intranuc. rhiz.) passes to the nuclear 

 membrane and thence (rhiz.) to the blepharoplast of its side at the 

 head of the axostyle, forming as it passes the nuclear membrane, an 

 anterior membrane granule. It is possible that this represents the 

 centrosome {cent., fig. A). There is a corresponding granule, the 

 posterior membrane granule at the opposite pole in some nuclei (pi. 5, 

 figs. 1, 2) which does not seem to be a second centrosome, judging 

 from the fact that it may appear when no indications of mitosis are 

 visible. 



These rhizoplasts arising from the central karyosomes are connected 

 with the blepharoplasts, the centers from which .starts the complicated 



