72 



ZOOLOGY 



SECT. 



flagellum (or one of them, if two are present) is attacked through- 

 out 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 

 varied modes of nutrition. Many of the lower forms, such as 

 Heteromita, live in decomposing animal infusions : they have 

 neither mouth nor gullet and take no solid food, but live by 

 absorbing the nutrient matters in the solution ; their nutrition is, 

 in fact, saprophytic, like that of many fungi. A few live as para- 

 sites in various cavities of the body of the higher animals. The 

 Hwmoflagellata, an extensive group, live as parasites in the 

 plasma of the blood of various vertebrates. Most of these appear 

 to be harmless, but some are the causes of serious diseases in Man 



Fio. 53. — Trypanosomes of Fishes, c. blepharoblast ; /. flagellum ; fa, and fp. (In k) anterior 

 and posterior flagella ; m. undulating membrane ; n. nucleus. (After Laveran and Mesnil.) 



and other higher animals. One Euglena-like form lives as an 

 intra-cellular parasite within the cells of one of the lower worms. 



Hcematococcus (Fig. 54), Pandorina (Fig. 55), Volvox (Fig. 56), 

 and their allies present us with a totally different state of things. 

 The mouthless body is surrounded by a cellulose cell-wall (cm.), 

 and contains chromatophores (chr.) coloured either green by chloro- 

 phyll or red by haematochrome. Nutrition is purely holophytic, 

 i.e. takes place by the absorption of a watery solution of mineral 

 salts and by the decomposition of carbon dioxide. It is, there- 

 fore, not surprising that these chlorophyll -containing Flagellata 

 are often included among the Algse or lower green plants. 



Other genera live in a purely animal fashion by the ingestion of 

 solid proteinaceous food, usually in the form of minute living 

 organisms : in these cases there is always some contrivance for 

 capturing and swallowing the prey. In Oikomonas (Fig. 52, 8), 

 we have one of the simplest arrangements : near the base of the 

 flagellum is a slight projection containing a vacuole (v.i.); the 

 movements of the flagellum drive small particles (/.). against this 

 region, where the protoplasm is very thin and readily allows the 

 particles to penetrate into the vacuole, where they are digested. 



