MASTIGOPHORA: FLAGELLATA. 843 



vacuoles occur when the food is ingested by means of a vacuole, rarely 

 in other instances. Indigestible remnants are expelled at the hinder end 

 of the body as a rule, rarely anteriorly as in Bicosoeca, or in amoeboid 

 forms at arty spot. A contractile vacuole is seldom absent. It is usually 

 single, rarely double, more rarely multiple. It is constant in position 

 except in the amoeboid condition, and is frequently placed at the base of 

 the flagellum or laterally ; it is superficial except in some Euglenoids 

 where it debouches into a reservoir opening in its turn into the oeso- 

 phagus. 



The nucleus has not been observed in some of the smallest forms. 

 It is typically vesicular, and in Euglenoids often reticulate with or without 

 a nucleolus. Trepomonas has two nuclei, other Flagellata only one. A 

 diffuse colouration of the protoplasm never occurs. Chromatophores, 

 always superficial in position, are common in certain groups, e. g. Isomas- 

 tigoda. They are firm, soft, of definite shape, and consist of a colourless 

 basis infiltrated with green chlorophyl or brown diatomin, or a mixture of 

 both substances in variable proportion ; hence a corresponding variation 

 in their tint. They multiply by fission. They are numerous, small, round, 

 or oval in Euglenoids, two in number, large and plate-like in Dinobryon^ 

 &c. ; single and enveloping the whole surface in Chlamydomonas, Gonitim, 

 and probably in other Chlamydomanadina and Volvocina. Allied forms 

 may be coloured or colourless, e.g. Chlamydomonas and Polytoma, -Crypto- 

 monas and Chilomonas ; and colourless species may occur in coloured 

 genera, e. g. Euglena *. Clear bodies, one or more, known as pyrenoids or 

 amylum-bodies, are found in connection with the chromatophores of some 

 Euglenoids, of Chlamydomonads and Volvocina. They multiply by 

 fission and consist of a core, the pyrenoid, a clear substance which stains 

 readily, coated in nearly all instances with starch or amylum, rarely with 

 paramylum. Starch granules have been observed scattered in the proto- 

 plasm of Cryptomonas as well as in some colourless saprophytic forms when 

 well nourished, e. g. Chilomonas. Paramylum, a substance of the same cen- 

 tesimal composition as starch, but not stained by iodine, occurs as laminated 

 grains of varying size, oval, rod- or ring-like in shape, in the protoplasm 

 of Euglenoids 2 . When the green-coloured organism passes into a rest- 

 beyond doubt, and it possibly occurs in other instances. Some colourless forms (septic monads) 

 have been observed to take in solid particles in quantity when in an amoeboid state. Bodo caudatus 

 is able to pierce the cuticle of Chlamydomonas, and even of Infusoria, and to suck out the contents 

 by means of its mouth. 



1 Polytoma and Chilomonas live in putrifying solutions, and are saprophytic, as are also 

 colourless Euglenae. Chlorogonium and Carteria (Chlamydomonads) are said to become colourless 

 tinder conditions in which they may be saprophytic. 



2 For the characters of paramylum, see Biitschli, Protozoa, Bronn's Thierreich, i. pp. 727-30. 

 Amyloplasts, or starch-builders, are said to be present in Chilomonas (Fisch, Z. W. Z. xlii. 1885, 

 p. 82). For these starch-builders, see Sachs' Lectures on Physiology of Plants, transl. by Ward, 

 1887, p. 316, and Schimper, Q. J. M. xxi. 1881. 



