212 SOME MINUTE ANIMAL PARASITES 



development within the silkworm were not worked 

 out, the interest at the time centring around the 

 economic side of the work rather than the purely 

 scientific. 



Since the time of Pasteur, many organisms allied 

 to the Nosema of pebrine have been discovered, and 

 some fish tumours and wasting diseases of other 

 insects have been found to be due to members of the 

 same group, the Microsporidia, or to the nearly 

 related group, the Myxosporidia. An interesting 

 point in connexion with the distribution of the 

 two groups is that the Microsporidia seem to have 

 advanced farther along the road of parasitism than 

 the Myxosporidia. Certain of the Microsporidia, 

 such as the Nosema bombycis of the silkworm, have 

 developed both enormous powers of multiplication 

 within one host and a capacity for invading and 

 dwelling within each and every tissue and organ of 

 the animal that shelters them. N. bombycis occurs 

 in the alimentary tract, fat-body, muscles, circula- 

 tory system and reproductive organs of its host, 

 and is easily able. to multiply in all of them, thereby 

 showing great powers of adaptation to the very 

 different media by which it is surrounded. Many of 

 the Myxosporidia, on the other hand, have a more 

 restricted distribution, and in many cases are found 

 parasitic in the gall-bladders or kidney tubules of 

 their hosts, or more rarely in skin tumours. 



Thanks to the preventive measures adopted in 

 France, pe"brine among silkworms has practically dis- 

 appeared, and to the present generation of French 

 scientists and silkworm rearers, pebrine belongs to 



