I04 PROTOZOA. 



DIAGRAM IV. 



The Classes of Protozoa. 



In the lowest line the life-cycle of Protomyxa is represented. The 

 median figure {pi.) is a plasmodium ; to the right is the encysted phase 

 {enc. ), within which the protoplasm divides into many units or spores 

 \sp. ). To the left the cyst bursts, liberating flagellate spores (fl. ), which 

 sink down into amoeboid units {am. ), from the coalescence of which a 

 Plasmodium results. The phases of this life-cycle furnish the key to the 

 whole classification. 



In the next line are examples of the three great divisions. In the 

 middle, is an Ammba {A.), with nucleus («. ), granules {g.), contractile 

 vacuoles {c. v.) ; it is about to engulf a small particle of food {/d. ). To 

 the right side, is a Gregarine with its substance divided by a partition {p. ), 

 with a caducous cap (<r. ) at the anterior end. The next figure {m. ) to the 

 right is another Gregarinid, without a partition, but with numerous 

 transverse fibrils. To the leftside, is the cup of Vorticella {v.), showing 

 the anterior cilia, the curved nucleus («.), the beginning of the stalk (st.) 

 with its central axis. P'urther to the left is Paramccciutn, with macro- 

 nucleus (k.) and micro-nucleus beside it, with mouth (/«.) and food- 

 particles entering, with contractile vacuoles U. v.), with food- vacuoles 

 round the nutritive particles, with cilia {c) on the surface. 



Follow the median division upwards. The young Amceba {yg. ) grows 

 larger (gr.), divides into two {div.). Conjugation (conj.) has been 

 observed. Encystation occurs {enc), and rejuvenescence {rej.) when the 

 cell escapes from its cyst. 



Follow the history of a Gregarine. The young forms {yg.) are usually 

 intra-cellular parasites. Sometimes individuals unite in a strange end- 

 to-end fashion {conj. ?) ; sometimes two fuse and encyst {conj. ). Within 

 the cyst (enc.) spores are formed {sp.), one or more in each of the many 

 spore-cases {sp. c. ). The cyst bursts, the spore-cases open, the young 

 forms {yg.) may be slightly amoeboid, as the topmost line suggests. 



Follow the history of Vorticella. It divides longitudinally {div.), and 

 the halves separate ; or one-half may divide into 8 minute units {mi.). 

 A small individual conjugates with one of normal size (conj.). Encys- 

 tation (enc.) may occur, and the cup may free itself from its stalk (fr.). 



The young Paramacium (yg.) grows (gr.) and divides (div.). In 

 conjugation (conj.) the micro-nucleus divides into 8, the macro-nucleus 

 (left light in this figure) degenerates. After conjugation and subsequent 

 separation (topmost figure) the nuclei are reconstructed. 



