INTRODUCTION. 



plate and an indication of spindle-fibres converging at the poles ; 

 at a later stage the swarni-cell becomes ellipsoid and a constriction 

 appears in the middle. As bipartition proceeds the nuclear plate 

 divides and the two halves separate, the connecting achromatic 

 fibres being often discernible. The daughter-nuclei at length 

 retreat to the opposite poles of the swarm-cell, which in about a 

 quarter of an hour from the beginning of the process of con- 

 striction is completely divided. A flagellum is in a short time 

 produced by each daughter -cell, which then assumes the original 

 form of the parent. After dividing in the manner described, 

 through a period of uncertain duration, they withdraw the 

 flagellum and creep with slow amoeboid movement. When two 

 of them come in contact with each other they may coalesce ; 

 others congregate at this point and form a centre to which great 

 numbers converge, and though they may remain distinct for 

 some time, ultimately unite and mingle into one moving mass, 

 the plasmodium of Cienkowski. 

 There is no doubt that the 

 young plasmodia exercise a 

 distinct attracting influence 

 on the swarm-cells in their 

 neighbourhood. Many amoe- 

 boid swarm-cells, after re- 

 maining some time near the 

 plasmodium, contract and form 

 into microcysts, in which state 

 they are enclosed by the plas- 

 modium and become sur- 



rounded with vacuoles, where 

 they are gradually digested. 

 Although the fusing swarm- 

 cells thus lose their individu- 



ality, their nuclei, SO far as swarm-cells, some of which have turned ii 

 i-i T i microcysts (//i) : one microcyst is being digest 



has been obser\ecl, remain in a v / cuol ^ ^ An empty spore-shell is Ixo 



FlG. 3. DlDYMIUM DIFFORME Dubj. 



Young plasmodium, with attendant amoeboid 



ned into 

 digested 

 is shown 



distinct. For example, eight at *. 



,. , Magnified 470 times. 



swarm-cells may be counted 

 uniting and forming a plas- 

 modium, and their eight nuclei can be afterwards distinguished ; 

 but when this number is exceeded the movements of the plas- 

 modium and the inconspicuous nature of the nuclei present 

 difficulties in the way of their recognition. Whatever reason 

 there may be from general considerations to regard this fusion 

 of individuals as akin to conjugation, no fusion of nuclei, which 

 appears to be an essential part of the process, has yet been 

 observed. 



In the Exosporece represented by the single genus Ceratiomyxa, 

 the spore is ellipsoid, and consists of granular protoplasm, in 

 which four nucleus-like bodies can often be observed. This is 

 enclosed by a membranous and colourless spore- wall. On placing 

 the perfectly matured spores in pure water, the membranous 



