INTRODUCTION. 3 



produced abundant swarm-cells in twenty-eight hours, after three 

 years and nme months from the date of collection, and in a few 

 days all the spores appeared to have germinated, and plasmodia 

 were formed in a moist chamber. Sporangia were developed 

 eleven days after the sowing of the spores. The spore-waU is 

 ruptured by the swelling of the contents, which slowly emerges 1 

 through the opening, and in about ten minutes lies as a nearly 

 pellucid globule by the side of the empty membrane; after 

 remainmg quiescent for a few minutes amoeboid movements begin 

 to take place, and shortly afterwards the flagellum is produced. 

 This is at first a somewhat tentative process, and the flagellum 

 IS frequently withdrawn ; but in about a quarter of an hour it 

 acquires its full length of about 15 /t, and by its lashing strokes 

 the swarm-cell swims off with a dancing movement. At this 

 stage it is pyriform in shape, the interior body-substance is 

 granular and contains a con- 

 tractile vacuole, and often one 

 or more vacuoles in addition 

 which do not usually show con- 

 traction. At the narrow end 

 is placed the nucleus, which 

 can easily be recognised by its 

 lighter and. more homogeneous 

 appearance and central nucle- 

 olus. The nucleus does not 

 alter its position, though con- 

 stant movement is observed 

 among the constituents of the 

 granular part. The whole is 

 enclosed by a layer of hyalo- 

 plasm devoid of granular par- 

 ticles, and of extreme tenuity 

 over most of the surface, but 

 thicker at the anterior end, 

 where it is produced into the 

 flagellum immediately in front 

 of the nucleus, and also at the 

 posterior end, where it often 

 extends in a brush of two to eight more or less slender pseudopodia. 

 In addition to the dancing motion, which is maintained as long as 

 they are free in the water, the swarm-cells when they come to rest 

 exhibit movements of an amoeboid character, and spread with an 

 irregular outline ; or they assuine a linear form and creep over a 

 level surf ace_ with a snail-like motion, the flagellum being extended 

 in advance.' In this position the movement of the interior 

 substance is seen to advantage. In the large swarm-cells of 

 Amaurochmte atra it may almost be described as streaming, the 

 granules passing from one end to the other ia constant flow ; 

 the hyaloplasmic extension at the posterior end continually 

 changes its form and often detaches portions which cannot 



Fig. 1. — DiDYMicM diffobme Duby. 



6. Swarm-cell escaping from the spore-case. 



c. Newly hatched swarm-cell containing a 



nucleus and three Tacuoles. 



d. Flagellated swarm-cell. ' 



e. Swarm.-cell, with two vacuoles containing 



bacteria,, and produced at the posterior 

 end into pseudopodia, to one of which a 

 bacterium is at^ched. 



/. Amoeboid swarm-cell. 



Magnified 720 times. 



