FLAGELLATA. 21 



The Flagellata are allied to certain fungi. They are animals, 

 because the body and the flagella are contractile ; they are cap- 

 able of voluntary movement ; they possess excretory organs in 

 the form of contractile vacuoles ; and, moreover, they are pro- 

 vided, unlike Amceba, with a more or less definite space for a 

 mouth. One family of them, the Monadinm, are found in putre- 

 fying infusions, and are exactly like fungoid monads. Two 

 genera. Trichomonas and Cercomonas (fig. 3, ii.), which are pro- 

 vided with whip-like flagella, may be found in abundance in 

 the intestines of vertebrates. Eeproduction takes place by 

 transverse fission, the flagella being first withdrawn within the 

 membrane prior to the nucleus dividing. When that stage is 

 completed, the protoplasm divides, and then the whole organism 

 splits transversely across, forming two flagellata, which soon 

 protrude their flagella and become active (iii.) Eeproduction in 

 the Flagellata also takes place by spore formation ; the protozoon 

 draws in its flagella and becomes encysted : when in the en- 

 closed stage, the protoplasm, following the rapid division of the 

 nucleus, forms around each new nucleus a round mass, which 

 develops a hard shell or coat, and so produces a spore. Hun- 

 dreds of these spores may be formed from one individual. This 

 spore formation is always preceded by the conjugation of two 

 individuals, similar to what we observed in Amoeba. 



The Flagellata are divide'd into four sub-classes, as follows : — 

 i. Ltssoflagellata. — With no collar - like outgrowth around 



the oral pole, 

 ii. Qhoanoflagdlata, — Flagella provided with a collar sur- 

 rounding the anterior pole of the celL 

 iii. Dinoflagellata. — Provided with a longitudinal groove and 

 a flagellum projecting from it, and also a transverse 

 groove in which lies a second flagellum. 

 iv. Ehyndioflagellata. — Provided with reticulate protoplasm 



(marine). 

 Trichomonas and Cercomonas both belong to sub-class L 

 One species of Cercomonas — viz., gcdlinm — is often found in 



