134 SUMMAEY OF CURRENT KESEAKCUES EELATING TO 



tracting. The food consists for the most part of uniceUular Alga^, but 

 Protozoa are also used. The ciliary disk has apparently but one circlet 

 of cilia ; the membranous collar is moderately large, but obliquely set ; 

 the stalk of the colony shows profuse dichotomous branching. The 

 use of the term " polypidum " in reference to a colony of Protozoa is to 

 be deprecated. 



Fission in Hexamitus.* — Olive Swezy has studied the binary and 

 multiple fission in species of Hexamitus from the rectum and large 

 intestine of a number of Amphibians. In most cases H. intestinalis was 

 the species met with. It may be noted tiiat the genus is represented in 

 rats, mice, snakes, tortoises, and fishes, as Avell as in Amphibians ; and 

 that H. inflatus occurs in stagnant water. The flagella are so minute 

 that there has been prolonged uncertainty as to their number, which is 

 eight, not sis. 



The cell-division is a simple form of mitosis, initiated by division of 

 the blepharoplasts, followed by longitudinal splitting of both asostyles. 

 Four chromosomes are found on the mitotic spindle, two going to each 

 of the daughter-nuclei. New nuclear membranes are formed inside the 

 old one, which fades and disappears before the completion of the process 

 of cell-division. 



Multiple fission takes place in the unencysted forms by a series of 

 successive divisions of the two nuclei and the accompanying motor 

 apparatus without corresponding division of the cell-body, forming a 

 somatella of eight undivided binucleate individuals. These subsequently 

 break up by successive splitting off of one individual at a time. The 

 binuclear structure of the potential individuals is maintained throughout 

 the process. Both binary and multiple fission occur similarly in at 

 least two species, H. ovatus and H. intestinaUs ; multiple fission has 

 been observed in a third species, H. liatracJwrum. 



Monocercomonas and Polymastix.f — Olive Swezy has made a study, 

 of these two parasitic Flagellates from the food-canal of insect larvae 

 and Amphibians respectively. The generic characters of Monocer- 

 comonas 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 31. melolontlise (Grassi) and M. ceto7iise Jollos. 



The genus Polymastix differs from 3Ionocercomonas mainly in the 

 absence of an axostyle, the presence of striations on the definite periplast, 

 and, in most cases, the extranuclear chromidial l)odies or parabasal. 

 Ijodies. As M. bvfonis Dobell possesses the generic characters of 

 FohjmasHx, it should be called F. hiifonis (Dobell). 



The process of division in P. hufonis is a simple form of mitosis, 

 exhibiting two chromosomes, pole-plates instead of centrosomes, and the 

 formation of two nuclear membranes inside the old one, which dis- 

 appears. The parabasal body divides by a simple constriction. The 



* Univ. California Publications (Zool.) xvi. (1916) pp. 71-88 (3 pis.). 

 t Univ. California Publi'cations (Zool.) xvi. (1916) pp. 127-38 (2 pis.). 



