134 TJ niversiiy of California Publications in Zoologi/ [Vol. 16 



these fibrils could not be traced. Their absence during the stages of 

 mitosis of the nucleus would indicate their origin as later outgrowths 

 from either the nucleus or the blepharoplast. Some suggestions of 

 splitting of the parabasal rhizoplast are found in figures 13 and 15, 

 plate 17. 



The only division stages of this flagellate heretofore described have 

 been those figured by Alexeieff (1911), two figures similar to ones 

 shown herewith (pi. 17, figs. 16, 20), differing in no essential details 

 beyond the four and six blepharoplasts which he figures. 



Summary 



The generic characters of Monocercomonas are as follows: four 

 equal anterior flagella, arising from one or more blepharoplasts or 

 basal granules, a large vesicular nucleus situated at the anterior end, 

 a slender axostyle arising in the blepharoplast and terminating in the 

 periplast at the posterior extremity of the body. The only authentic 

 species are M. melolonthae (Grassi) and M. ceioniae JoUos. 



The genus Polymastix differs from Monocercomonas mainly in the 

 absence of an axostyle, the presence of striations on the definite peri- 

 plast, and, in most cases, the extranuelear chromidial bodies or para- 

 basal bodies. 



Monocercomonas bufonis Dobell possesses the generic characters of 

 Polymastix, hence should be placed in that genus as P. bufonis 

 (Dobell). 



The process of division in Polymastix bufonis is a simple form of 

 mitosis, exhibiting two chromosomes, pole plates instead of centro- 

 somes and the formation of new nuclear membranes inside the old one 

 which disappears. The parabasal body divides by a simple constric- 

 tion. The division of the cytoplasm begins at the anterior end and 

 proceeds posteriorly. 



This forms part of a series of investigations on protozoan parasites 

 carried on in the protozoologieal laboratory of the University of Cali- 

 fornia imder the direction of Professor Charles Atwood Kofoid, to 

 whom the writer is much indebted for helpful suggestions and 

 criticisms. 



Transmitted November 30, 1915. 



Zoological Laboratory, 



University of California, 



Berkeley, California. ^ 



