272 



THE PROTOZOA 



organism rather than as distinct generic types. Trichomonas hominis is 

 ontozoic in the human intestine, T. vaginalis in the human vagina ; they 

 appear to be harmless scavengers rather than parasites. The encystment 

 of Trichomonas has been the subject of some controversy. According to 

 Alexeieff (326), the supposed cysts of Trichomonas described by various 

 authors are in reality independent vegetable organisms, of the nature 



of yeasts. In some species of Trichomonas the 

 anterior flagella are four in number (Alexeieff, 

 323) ; for such forms Parisi (A.P.K., xix., 

 p. 232) has founded a subgenus Tc.tr atricho- 

 monas. The genus Macrostoma, according to 

 Wenyon (362), differs from Trichomonas in 

 having the undulating membrane wedged in 

 a deep groove ; M . mesnili occurs in the 

 human intestine. According to Alexeieff (324), 

 Macrostoma ig a synonym of Tetramitus. Mono- 

 cercomonas, including a number of common 

 intestinal parasites, has four anterior flagella 

 of equal length, or two longer, two shorter 

 (Alexeieff, 325). 



Costia necatrix, also referred to this family, 

 is ectoparasitic on the skin of fishes. According 

 to Moroff, it has four flagella in two pairs, two 

 larger and two smaller, all of which serve for 

 locomotion ; but the larger pair are used also 

 for fixation, and the smaller pair for wafting 

 into the mouth the food-particles, which consist 

 chiefly of dead epithelial cells torn away from 

 the epidermis (see also Neresheimer). 



2. Octomitidce.* With six or eight flagella, 

 arranged in pairs ; the body is bilaterally 

 symmetrical in structure. Entozoic forms, for 

 the most part of intestinal habitat. 



The remarkable bilateral symmetry of the 

 species of this family is not merely an external 

 characteristic of the body, but affects the 

 internal structure as well, and the entire 

 nuclear structure is doubled, with right and left 

 halves. Octomitus (synonym, Hexamitus ; see 

 Dobell, 236), with four pairs of flagella (Fig. 116), 

 includes a number of entozoic species e.g., 

 0. intestinalis, from the cloaca of the frog and 

 other animals. Lamblia intestinalis (synonym, 

 Megastoma enter icum, Pig. 117) is a common 

 inhabitant of the human intestine. It becomes 

 encysted, and is probably disseminated in this 

 form. Within the cyst it divides into two 

 (Rodenwaldt). L. sanguinis, described by 

 Gonder (A.P.K., xxi., p. 209) from the blood 

 of a falcon, is probably an intestinal parasite 

 gone astray (vide p. 258). 

 The order Polymastigina differs little from the Protomonadina except in 

 the complication of the flagellar apparatus, correlated probably with the 

 entozoic habit. Hartmann and Chagas propose to merge the Polymastigina 



* Doflein terms this family the Polymastigidai, but the name is clearly in- 

 admissible, since the genus Polymastix belongs to the preceding family, and is 

 closely allied to Trichomonas, but has six anterior flagella and no trailing 

 flagellum (compare Alexeieff, 325). 



Fio. 116. Octomitus dujar- 

 dini. W. 1 , Anterior blep- 

 haroplast, from which the 

 first and second flagella of 

 that side of the body arise ; 

 W. 2 , second blepharoplast, 

 giving off the flagellum of 

 the third pair ; #., left-hand 

 nucleus ; ax., left axostyle ; 

 U. 3 , third blepharoplast, at 

 the extremity of the axo- 

 style, giving off one of the 

 flagella of the fourth pair. 

 All the structures indicated 

 are paired, and the letters 

 indicate the member of each 

 pair on the left side of the 

 body. After Dobell (236). 



