32 



PEOTOZOA 



[CH. 



water, and drag the animal after them by a spiral screw-like motion, 

 just as a steamship is dragged by the screw when the engines are 

 reversed. These flagella as we have already seen are carried by the 

 germs of some Thalamophora, Mycetozoa and Radiolaria, but in the 

 Flagellata they are permanent. In many cases where the matter 

 has been closely investigated each flagellum is seen to originate in 

 a minute basal granule. We may take as a type Euglena viridis, 

 one of the numerous inhabitants of ditches. This animal has a 

 narrow elongated shape, pointed at one end, and at the other, 

 which is its front end, it possesses a minute pore, which passes 

 through the outer stiffer layer of protoplasm, and at the bottom of 

 which the soft inner protoplasm is exposed. This is termed the 

 pharynx and it is exceedingly narrow. It has a flagellum which 



FIG. 10. Euglena viridis. 



A x 100, B, C, D, E, F x 200 showing the different shapes assumed by the 

 animal during the euglenoid movements. 1. Pharynx. 2. Contractile 

 vacuole. 3. Pigment spot. 4. Nucleus. 



arises from its wall near its inner end. Slightly behind the pharynx 

 there is a small clear vacuole, and at the one side of this a small 

 red spot, which may very possibly be associated with a sensitiveness 

 to light. The clear vacuole opens into the pharynx ; it is termed 

 the reservoir for two contractile vacuoles lie behind it and discharge 

 into it. About the middle of the body is a nucleus which can 

 sometimes be made out as a clear spot in the living animal, but 

 which is most satisfactorily observed when the animal is killed with 

 osmic acid and stained with picrocarmine. 



t Two features in Euglena, however, will strike us as very peculiar. 

 One is, that in spite of possessing a permanent cuticle it is able to 

 change its shape. It does not possess the power of throwing out 

 pseudopodia, but it bends its body in the most extraordinary way, 



