WHAT A NOSEMA SPORE PRODUCES 225 



the cavity of the gut and burst there, they remain 

 inactive unless taken up by another bee, or, perhaps, 

 a wasp. Once again swallowed with food, the spores 

 rarely undergo change till they reach the chyle 

 stomach of the host. Then, under the influence of 

 the digestive juices, the sporocyst of each spore 

 softens. At the same time, the movements of the 

 digestive tube render some sort of anchorage neces- 

 sary. The polar filament is shot out vigorously, and, 

 penetrating between the cells of the epithelium, fixes 

 the spore for the time. The sporoplasm now moves 

 forwards, and as it presses around the polar capsule, 

 and begins to leave the spore through the aperture 

 made by the polar filament, the latter structure is 

 often snapped off, or forced completely out of the 

 cell (Fig. 41, E) in front of the issuing amoebula. 

 Empty "shells" are then to be found, mingled with 

 food debris, and can be easily recognized as empty if 

 they are compared with the glistening, opaque spores, 

 whose brilliancy is far greater than that of the empty 

 spore. 



The size of the oval spore may be gathered from 

 the fact that it is about ^Vo of an inch long, and that 

 its breadth is about half its length that is, in terms 

 of measurement used in microscopy, the dimensions 

 of a Nosema spore average 5 /j, by 2*5 /*. 



The life-history of Nosema apis is largely confined 

 to the alimentary tract, but N. bombycis of the silk- 

 worm, which has a life-cycle similar to that of the 

 bee parasite, is more deadly than the latter, for it has 

 acquired the power of invading every part of the 

 body and of developing fully therein. N. apis is 



