72 ZOOLOGY SECT. 



the Flagellata. It is placed among the Euglenoidea in virtue of 

 possessing a single flagellum and a small gullet into which 

 the reservoir opens. The genus Euglena is distinguished 

 by its centrally placed nucleus, green chromatophores, red stigma, 

 and euglenoid movements. E. viridis is separated from other 

 species of the genus by its spindle-shaped body with blunt anterior 

 and pointed posterior end, and by the flagellum being somewhat 

 longer than the body. 



ORDER 1. FLAGELLATA. 



In the Flagellata the cell-body is usually ovoid or flask-shaped 

 (Fig. 53, 6, 7, 9, &c.), but may be almost globular (1), or greatly 

 elongated (3). Anterior and posterior ends are always distinguish- 

 able, the flagella being directed forwards in swimming, and, as a 

 rule, dorsal and ventral surfaces can be distinguished by the presence 

 of a mouth or by an additional flagellum on the ventral side. They 

 are, therefore, usually bilaterally symmetrical, or divisible into equal 

 and similar rightfand left halves by a vertical antero-posterior plane. 



Some of the lower forms have no distinct cuticle, and are able, 

 under certain circumstances, to assume an amoeboid form (2). 

 The curious genus Mastigamceba (4) has a permanently amoeboid 

 form, but possesses, in addition to pseudopods, a single long 

 flagellum. It obviously connects the Mastigophora with the 

 Rhizopoda, and indeed there seems no reason why it should be 

 placed in the present group rather than with the Lobosa. Simi- 

 larly, Dimorpha (<5) connects the Flagellata with the Heliozoa : in 

 its flagellate phase (a) it is ovoid and provided with two flagella, 

 but it may send out long stiff radiating pseudopods, while retaining 

 the flagella, or may draw in the latter and assume a purely helizoan 

 phase of existence provided with pseudopods only (6). 



Nuclei of the ordinary character are universally present. In 

 addition there may be present in the cytoplasm at the base of the 

 flagellum or of each flagellum a very much more minute body which 

 is termed the blepharoplast (Fig. 54, 6), and in close relation to 

 the latter is a secondary nucleus or Jcinetonucleus (Jc.n). 



The number of flagella is subject to great variation. There 

 may be one (Fig. 53, 1-3), two (9, 10), three (6), or four (7). 

 Sometimes the flagella show a differentiation in function ; in 

 many cases in which two flagella are present one only is used in 

 progression, ^the second or ventral flagellum is trailed behind when 

 the animal is swimming freely, or is used to anchor it to various 

 solid bodies. In some (Trypanosomes, Fig. 54) the flagellum (or 

 one of them, if two are present) is attached throughout its length, 

 or in the greater part of its length, to the edge of a wavy protoplasmic 

 flange, or undulating membrane, running along the body. 



There are also important variations in structure correlated with 



