Animal Life and Intellige^ice, 



the relatively large, sluggish, parasitic Gregarina, to the 

 active slipper-animalcule, or Pai^amoecium, or the beautiful,, 

 stalked bell-animalcule, or Vorticella ; and from the small, 

 slow-moving amoeba to the minute, intensely active monad. 

 In many cases reproduction is by simple fission, as in the 

 amoeba, where the nucleus first undergoes division; and 

 then the whole organism splits into two parts, each with 

 its own nucleus. In other cases, also numerous, the 



d 



Fij?. 



-i'rotozoa. 



A, vorticella extended. B, the same contracted. C, D, monads. E, amoeba. F, Para- 

 mecium. G, Gregarina. c/., contractile fibre ; c.v., contractile vesicle ; (i.,disc ; end., endo- 

 plast ; f.v., food-vacuole ; jl., flagellum ; gu., gubernaculum •, «., nucleus ; ^.a., potential anus v 

 ps., (in A) peristome, (in E) pseudopodium ; vs., vestibule. 



organism passes into a quiescent state, and becomes sur- 

 rounded with a more or less toughened cyst. The nucleus 

 then disappears, and the contents of the cyst break up 

 into a number of small bodies or spores. Eventually the 

 cyst bursts, and the spores swarm forth. In the case of 

 some active protozoa the minute creatures that swarm forth 

 are more or less like the parent ; but in the more sluggish 

 kinds the minute forms are more active than the parent. 

 Thus in the case of the gregarina, the minute s^Dore- 

 products are like small amoeba3 ; while in other instances 



