1 6 PROTOZOA AND DISEASE 



various forms of colpoda, as we have it from von Rhumbler, 1 and 

 regard the forms evolved from the sporocysts provisionally as 

 involution-forms. When watched in a culture in hay-infusion, 

 Colpoda cucullus 2 passes through the following changes : 



Encystment before Division. The movements are slow, and the 

 animalcules, which are bean-shaped (Fig. 3; 7), become rounder; 

 progression ceases whilst rotation continues ; a gelatinous secretion 

 exudes from the surface and hardens to a structureless cyst (Fig. 3 ; 2), 

 the contractile vacuole continuing to beat at the usual rate, four 

 times a minute, and, in spite of the animalcule rotating within the 

 cyst, the vacuole maintains a position opposite a minute pore in the 

 cyst-wall. Division begins by a constriction of the exterior of the 

 animalcule at right angles to its long axis (Fig. 3 ; 3} ; sometimes a 

 second constriction occurs at right angles to the first, resulting in 

 fourfold division (Fig. 3 ; 4) ; nuclear division accompanies this proto- 

 plasmic constriction. 



When the separation of the daughter animalcules is complete, 

 they escape through the opening in the cyst, making many attempts 

 before they finally succeed, owing to the smallness of the pore 

 (Fig. 3 ; 4). Should conditions not be favourable, the daughter 

 animalcules become re-encysted (Fig. 3 ; 5, 6} instead of escaping. 

 Darkness appears to favour, want of food to delay, division. The 

 addition of distilled water causes disintegration of the animalcules. 



Duration-cysts differ from the above in having no pore. Unen- 

 cysted colpodas die and disintegrate when rapidly dried, but if 

 slowly dried they expel food - stuffs from their body, undergo a 

 rapid rotation, and shed a gelatinous covering, which hardens to 

 a cyst (Fig. 3; 7). The contractile vacuole becomes irregular or 

 disappears, as do the cilia, when the cyst -wall becomes hard 

 (Fig. 3 ; 8). At this stage the animal will revive after being placed 

 in fresh water for three days. Colpoda appears to survive not 

 longer than three weeks' drying in summer. Division-cysts may be 

 transformed to duration-cysts by secondary encystment (Fig. 3 ; 0, 70). 



1 L. von Rhumbler, Zeitschr.fur Wiss. ZooL, 1888. 



' 2 Colpoda is said (Delage and He'rouard) to subdivide only when encysted. 



