28 PROTOZOA. 



means of pseudopodia in an amoeboid fashion, or there is a definite 

 spot at the base of the main flagellum Avhere the food enters : this 

 spot is either marked by a mouth-vacuole (Fig. 23 2Y>) into which the 

 food slips, or by the presence of a mouth-opening with or without 

 a pharyngeal continuation. The expulsion of undigested remains 

 of food appears to be localised and often to take place by the 

 bursting of a vacuole ; but the position of the temporary anus, 

 which seems to be variable in the different forms, has only been 

 determined in a few cases. Contractile vacuoles close to the body- 

 surface seem to be always present, and in the Ewjlenina they appeal' 

 to open into a receptacle which is in communication with the hind 

 end of the pharynx. Chromatophores of the same character and 

 function as those of plants are present in the holophytic forms, 

 and vary in colour from a light green to a brown (Chlorophyll and 

 Diatomin). They contain amylum bodies, which consist of a central 

 mass of a highly stainable plasma the pyrenoid and of an outer 

 zone of amylum. The pyrenoids may increase by division. Amylum 

 bodies are also found in colourless saprophytic forms. Paramylum, 

 a substance more nearly allied to cellulose, is sometimes present in 

 the protoplasm. Chromatophores may be present or absent in 

 closely allied forms, and even in the same form at different times ; 

 their presence is of no systematic importance. 



The nucleus is always single except in Ti-fpomonas, which some- 

 times has two. Stigmata as red pigment spots are often present 

 in the protoplasm, usually at the base of the flagellum. 



Reproduction takes place by fission, which is usually, if not 

 always, longitudinal, in both the active and resting state, and some- 

 times by continued fission (spore formation) in the resting state. 

 In the first case the fission may be into two, or by successive binary 

 fissions into four, eight, sixteen, or even thirty-two before the young- 

 separate. When the fission is into two, the flagella become doubled 

 in number before the body divides. The manner in which this 

 doubling occurs is disputed: very likely a new set of flagella and 

 of the other organs of the body is formed before the division occurs. 

 When the first binary fission is succeeded by others, the successive 

 fissions take place within the cuticle, while the animal continues 

 to move by the two original flagella which remain attached to one 

 of the products of fission. 



Finally reproduction may take place by continued fission (spore 

 formation), during the resting state (Bo<lo, Tetrai/tita). This has 

 been observed to follow conjugation. 



