BUBKINQBOM PROTOZOA. 



29 



forms, such as Monas, in which no cuticle is developed, no 

 special mouth-orifice is present, though the in- 

 gestion of food takes place at a more or less 

 definitely localized region at the base of the 

 flagellum, the food-particles drawn to the 

 organism by the currents established by the l-"^ 

 flagellum usually impinging at this point ; Jj^i 

 where, however, a definite cuticle or shell is 

 developed a definite mouth occurs, and in 

 some cases, as Euglena (Kg. 13, B), this leads 

 into a distinct tubular pharynx projecting some 

 distance into the interior. No hollow digestive 

 tract is, however, present, but the food-parti- 

 cles, after traversing the gullet, are received 

 directly into the protoplasm of the body, and 

 are digested there as in Amoeba. A localized 

 egestive region, situated usually towards the 

 posterior end of the body, has been ascer- 

 tained to occur in some species, but in no 

 instance is it a permanent orifice, as is the 

 case with the mouth. In addition to the nucleus, contractile 

 vacuole, and food-particles, other definitely organized particles, 

 such as starch-like granules and pigment-granules, may be 

 imbedded in the protoplasm. In Euglena the pigment is 

 green and resembles plant-chlorophyll, probably too possess- 

 ing a similar function. A red pigment-spot (stigma) is also 

 present in this and other genera at the base of the flagellum 

 and is supposed to be concerned in light-perception. 



The typical Flagellate is a free-swimming single organism, 

 but many forms are fixed, developing a stalk by which they 

 are fastened to foreign bodies ; the stalk may be very much 

 branched, each terminal branch supporting an individual, the 

 whole thus forming a colony, without, however, any differ- 

 entiation among the individuals. Free-swimming colonies 

 also exist, such for example as Volvox, in which a large 

 number of individuals are grouped together to form a spheri- 

 cal hollow colony. Each individual contains chlorophyll- 

 granules and a red stigma, and is provided with two fla- 

 gella by the action of which the entire colony is propelled 



Fig. 13. 

 A, Oikomonas 

 (after Butschli). 

 B, Euglena CUIUS. 

 G, Godosiga 

 (after Butschli). 



