PROTOZOA. 



transverse fission, and also by spore formation in an encysted condition; 

 the latter method seenis in many forms to be preceded by conju- 

 gation. The best known species are Cercomonas Duj. and Trichomonas 

 Donne, of which the first is characterised by the possession of a caudal 

 filament, while Trichomonas has an undulating row of cilia close to 

 the flagella, which are usually two in number (fig. 133). They live 

 principally in the intestines of "Vertebrates, but are also found in 

 Invertebrates. Cercomonas intestincdis Lauibl. and TricJwinonas 

 vaginalis Donne, are found in Man. 



The Monads,* which cannot be sharply separated from the 

 Jfonadina-, are simple cells free from chlorophyll, the swarm spores of 

 which usually pass into an amoeboid stage, and after receiving nourish- 

 ment enter upon a motionless stage characterised by the possession 

 of a firm cell-membrane. A number of them (Monas, Pseudospora, 

 ColpodeUa), the so-called Zoospores, are mastigopods resembling the 



niastigopods (swarm spores) of Myxo- 

 mycetes, and, with the exception of 

 Colpoddla, grow up to creeping Amoeba? 

 which protrude pointed pseudopodia. 

 In this stage they may also be simply 

 regarded as small plasmodia, especially 

 when, as in Fionas amyli, several masti- 

 FIG. 133. a, Cermmonat intesHnuii*. gopods fuse together to form the amoeba. 



LeucktrtT" ' ^""^ (Bfter R " The >' tlien take in Colpodetta without 



first entering the amoeba stage a globu- 



lar form, their surface develops a membrane, and in this cyst they 

 break up by division of protoplasm into a number of segments which 

 pass out as swarm spores and repeat the course of development 

 (Colpodetta pugndx to Chlamydomonas, Pseudospora volrocis). 



Other Monads, the so-called Tetraplasta (Vampyrdla, Xuclearia], 

 do not puss through the mastigopod (swarm spore) stage. Their pro- 

 toplasm during the inactive encysted stage gives rise by division into 

 two or four, to the same number of Actinophrys-like Amoeba 1 , of 

 which some, like Colpodella, suck their nourishment from alga cells 

 (Spirogyra, Oedogonia Diatomacea, etc.), and some envelope ex- 

 traneous bodies. 



In mode of nourishment and locomotion the monads are allied to 

 the Rhizopods, but also to lower fungus forms like Chytridium. 



* L. ricnkowski, " P.citrii^c xur Kontniss dor Monaden." Arclrh: fii>- 

 SKcrosJt. Anatomic., Tom. I., isitri. L. Cienkovvski, "Uber ralmellncocii und 

 einige Flagcllaten,'' Tom. VI., 1870. 



