8 



BRITISH MYCETOZOA. 



motion occasioned by the lashing movement of the flagellum. They 

 possess a single nucleus and a contractile vacuole. To a large extent 

 the swarm-cells feed on bacteria, which are caught by pseudopodia 

 projected from the posterior end of the body. The bacteria are 

 conveyed into the body-substance, where they are digested in 

 vacuoles which form round them ; there may be one or more 

 digestive vacuoles, each containing several bacteria at one time. 

 The swarm-cells rapidly increase in number by bipartition. When 

 this takes place the flagellum is first withdrawn, and the swarm-cell 

 assumes a globular form; it then elongates, and a constriction 

 occurs at right angles to the long axis. Meanwhile the nucleus is 

 passing through the process of division by karyokinesis, and in the 

 course of a few minutes the two halves of the nuclear plate separate 

 and retreat to the opposite ends of the constricted cell, which now 



d c j 



Fig. 2.— Amauroch^te atra Rost. 



a to/. Successive stages in bipartition ot 

 swarm-cell, accompanied by the divi- 

 sion of the nucleus by karyokinesis. 

 Magnified 1200 times. 



Drawn from stained preparations in 

 Canada balsam. 



Fig. 3.— DlDYMIUM D1FFORME Duby. 



Youngplasmodium, with attendant amceboid 

 swarm-cells, some of which have turned 

 into microcysts < ml : one microcyst is 

 being digested in a vacuole (i>). An 

 empty spore-shell is shown at s. Mag- 

 nified 470 times. 



divides into two ; each segment soon acquires a flagellum, and 

 resumes the former active state. 



Microcysts. I n all cultivations of germinating spores a number of the 



swarm-cells, after a short time of activity, become encysted in a 

 globular form as microcysts. In this state they may remain dry for 

 several days, but on water being added the cyst-wall is ruptured 

 and the contents creep out and assume again the motile condition. 

 Frequently the entire group of swarm-cells will change to microcysts, 

 and reawaken in the course of two or three days while still im- 

 mersed in water. A few days after the germination of the spores, 

 the process of bipartition, by which the number of the swarm-cells 

 has greatly increased, ceases. The majority now withdraw the 

 flagellum, and adopt true amceboid movements. These amceboid 



Plasmodium, bodies collect in clusters, and coalesce to form plasmodia, which may 



