RWPORT ON THE DISEASES OF SILKWORMS IN INDIA 19 



one, so that two planonts give rise to one. A discussion of this point, 

 however, is of too purely scientific interest to occupy us here 

 (Text-fig. A, 3-6). 



When the planont — now to be known as a meront — settles down 

 in the gut-wall it at once commences to divide. The nucleus first 

 divides into two and then the body surrounding the two nuclei 

 divides so that we get two organisms exactly like the original, only 

 smaller (Text-fig. A, 7-11). These meronts go on dividing with 

 great rapidity until the cell which the original planont entered 

 becomes full of meronts (Text-fig. A, 12-14). It is not certainly 

 known what causes the meronts to stop dividing— it may be lack 

 of food or lack of space, some outside stimulus, or it may be some 

 internal stimulus which determines when multiplication shall stop.* 

 Whatever may be the cause, a stage in the development of Nosema 

 comes when the meronts stop dividing. They do not spread to 

 surrounding cells or tissues : they seem to remain in the cell in 

 which the original planont came of rest. 



The meronts now proceed to turn into spores, each meront 

 forming one spore. A meront is round to oval in shape and has a 

 single nucleus. When it is about to become converted into a spore 

 it becomes a definite longish oval and a vacuole appears at one end 

 (Text-fig. A, 15-16). The nucleus undergoes a series of divisions 

 which need not be gone into here, and finally the thick spore-wall 

 is secreted round the meront (Text-fig. A, 17). A second vacuole 

 develops at the opposite end to the first one and the living substance, 

 containing two main nuclei and several — up to 5 — subsidiary 

 ones, forms a girdle round the inside of the spore-case. We have 

 then got back to what we started from — a ripe spore. 



If the spore remained where it was formed it would not do much 

 harm, nor would it accomplish much towards the multiplication of 

 the parasites either inside or outside the caterpillar's body. The 

 function of the spore in all the Sporozoa is to hand on the infection 

 from one host to another. The thick spore-case is a protection 

 against the drying up of the living contents while the spore is exposed 

 to unfavourable conditions outside the body of the host in which 

 it was produced. What then is the fate of the spore after it has 

 been formed in the cell of the gut-wall of the caterpillar ? If we 

 were dealing with a very heavily diseased caterpillar there would 

 be the possibility of its "dying and the spores being set free by the 

 decomposition of the body, but in the vast majority of cases this 

 may not happen. How then are the spores to reach the outside 

 and infect a fresh caterpillar ? In order to understand this we must 



* As spores and dividing meronts may be seen in the same cell (Plates III and VII, fig. 1), 

 it would appear to be something more subtle than mere lack of space or food that brings on 

 spore formation. 



