20 REPORT ON THE DISEASES OF SILKWORMS IN INDIA 



understand a little about the working of the gut-wall cells and the 

 peritrophic membrane. These cells ■ are continually budding of! 

 portions into the space between the gut-wall and the peritrophic 

 membrane (Plates III and VII, figs. 3 and 1). These buds are 

 supposed to be the bearers of the digestive juice produced by the 

 gut-wall. When a cell is infected with Nosema it continues to bud 

 off portions although very probably the production of the digestive 

 juice is seriously interfered with. Thus the spores produced in a 

 cell of the gut-wall may ultimately be shed into the space between 

 the gut-wall and the peritrophic membrane in one of the digestive 

 juice buds. Now the peritrophic membrane is a delicate tube 

 attached to the gut- wall by its anterior end at the line of junction 

 between the fore and mid gut (Text- figs. B and C). It hangs 

 freely in the lower part of the gut so that the spores liberated into 

 the space between the gut-wall and the peritrophic membrane can 

 pass down this space to the rectum — or that part of the gut where 

 the fseces are formed. There they become stuck to the outside of 

 the fsecal mass as a rule and so pass out of the body. When a 

 caterpillar is very heavily infected with pebrine and when the 

 infection has been running for some time, the peritrophic membrane 

 becomes very imperfect and full of holes so that the spores, shed 

 into the gut get mixed with the undigested leaf and so passed to the 

 exterior mixed with the dejecta, but in the early stages of infection 

 the peritrophic membrane is intact and the spores cannot and do 

 not pass through it but reach the outside as has been described above. 



So much then for a rough outline of the development of Nosema 

 bombycis inside the gut of a silkworm. If the original infection 

 ended with the transformation of the merohts into spores the 

 parasite would never be the terrible plague that it can be. Even 

 if hundreds of spores were eaten by a caterpillar only a relatively 

 slight infection would result, for not all the spores dehisce in the 

 gut and not all the planonts manage to reach the gut -wall. Thus 

 only at most, say, a few hundred gut- wall cells would get infected, 

 and as we have noted infection does not spread directly from one 

 cell to another. This would be the limit to the infection unless 

 the worm was constantly being reinfected. But this is not so : 

 once a caterpillar is infected the infection spreads inside the cater- 

 pillar. How is this effected % It is obvious that what is known 

 as auto-infection must occur, and careful investigation shows that 

 this actually does occur.* The spores which are shed from the gut- 

 wall cells into the space between the gut-wall and the peritrophic 

 membrane may be ripe and ready to dehisce, in which case the 

 necessary stimulus is present in the digestive juice, the spores shoot 



* See Kudo (1916) on the subject of auto -infection. 



