.REPORT ON THE DISEASES OP SILKWORMS IN INDIA 21 



out their polai filaments and the planonts issue from the spore- 

 cases and attack the gut cells. This is the stage, I believe, when 

 tissues and organs outside the gut get infected. The planonts 

 which escape into the lumen of the gut at this stage do not have to 

 penetrate the peritrophic membrane in order to reach the gut-wall. 

 They are already in close contact with the cells of the gut. They 

 thus readily penetrate the gut-wall, and they have sufficient initial 

 energy — since it was not used up in traversing the peritrophic 

 membrane — to enable them to make their way through the basal 

 membrane and so into the cavities (hsemocoele) round the gut whence 

 they can attack the different tissues and organs that lie in these 

 spaces (Text-figs. B and C). Of course some planonts as before 

 settle in the gut-wall cells. When these planonts come to rest, 

 be it in the gut-wall, in the silk-gland, or in fat-body, they repeat 

 the history we have already outlined : they multiply abundantly, 

 forming nests of meronts which finally change into spores. 



Now the reproductive organs lie in the hsemocoele, and therefore 

 when planonts of Nosema bombycis enter this space these important 

 organs may become infected. It is in this way that pebrine is an 

 inherited disease. The sperms or " male seed " are riot liable, to be 

 attacked : the testis, or organ which produces the- sperms, may be 

 infected, but the sperms themselves are either too tiny or are in 

 some other way unsuitable, for I have never observed any disease 

 in them or in the cells that produce them even when the surrounding 

 tissues of the testes were heavily infected. The eggs, too, are not 

 easily infected except in the young stages ; the protective envelopes 

 that surround the eggs develop fairly early and the planont cannot 

 penetrate these, while the chance of a planont entering the micropyle 

 of the egg is very remote. In the early stages of development, 

 however—those stages which are passed in the caterpillar and early 

 pupa — infection can and does take place. 



Difficulty of observation here makes one cautious and the follow- 

 ing statement must be regarded as only approximately correct and 

 complete. On entering an egg the planont does not develop so 

 rapidly as in other tissues. It seems either to lie dormant or almost 

 at once forms spores : possibly the food substances present in the 

 egg at this stage are not readily available and the parasite cannot 

 obtain the required nourishment. The parasite is not, so far as 

 my experience goes, found in any numbers in unlaid eggs : the most 

 heavily infected pupae can be searched with the greatest care without 

 finding more than the very, slightest infection in the eggs. After 

 the eggs have been fertilized and laid, however, and once the eggs 

 start developing, the parasite goes" ahe^d for a time. It is probable, 

 I think, that when the yolk of the egg is being made available for 



