352 



SPOBOZOA. 



becomes detached. The binucleated sporoplasm creeps out 

 through the opening of the capsule {H), and the remaining two 

 nuclei degenerate in the spore. The two nuclei in the amoebula 

 fuse into one and the uninucleate planont is formed. The 

 entire life-cycle may be completed in four days. 



Dimensions. — Planont O-B-l-Sfiin diameter ; meront about 

 3-5 ju. in diameter; spore 3-4 jj, by 1-2/x ; polar capsule 

 1-5-2 /A by 0-8-1 /a; length of extruded filament 51-12 ^i, 

 or even up to 98 ;u.. 



Pig. 174. — Life-cycle of Nosema bombycis Nageli. I, extracellular 

 stages ; II, intracellular stages. A, planonts ; B, meront; 

 C, binary fission of meronts; Z), multiple division of meronts ; 

 E, stages in spore formation ; F, ripe spores in the mid- 

 gut of a new host ; G, extrusion of the polar filament ; 

 H, amcebula leaving the spore. (From Kudo, after 

 Stempell. ) 



Remarks. — Ohshima (1927), discussing the function of the 

 polar filament of the spore of Nosema hombycis, showed that 

 as soon as filament extrusion is accomplished in the midgut 

 of a silkworm the spore discharges a viscous fluid through 

 the tube of the filament, which remains hanging in a spherical 

 drop at the extremity of the filament. He has now shown 

 (1937) that the polar filament is a germination tubule. In 

 order to germinate the amoebula in the alimentary canal the 

 spore evaginates its filament through the peritrophic membrane 



