412 THE PROTOZOA 



united the Microsporidia with the Myxosporidia into a single order 

 the Myxosporidia (sensu latiori) which was divided by him into 

 two suborders : Phsenocystes ( = Myxosporidia sensu strictiori) and 

 Cryptocystes (= Microsporidia). This classification is found in 

 many textbooks ; but in view of the possession of polar capsules by 

 other orders of the Cnidosporidia, it is more convenient to maintain 

 the old order Microsporidia of Balbiani. 



The Microsporidia first attained an unenviable notoriety through 

 the ravages caused by Nosema bombycis, the cause of " pebrine," or 

 silkworm-disease ; hence the spores are often spoken of as " pebrine- 

 corpuscles." The silkworm-disease was investigated by Pasteur, 

 who found that the silkworms acquired the infection in two ways : 

 first, by the contaminative method, by eating leaves contaminated by 

 the faeces of other infected caterpillars, and thus infecting themselves 

 with the spores of the parasite byway of the digestive tract; secondly, 

 by the so-called " hereditary " method that is to say, through 

 the parasite penetrating into the ovaries and eggs of the female 

 silkworm-moth, and, in the form of spores, remaining dormant in 

 the egg through its embryonic development until the hatching of 

 the caterpillar, which in this way is born infected with the disease. 

 In contrast with the Myxosporidia, the Microsporidia are chiefly 

 parasites of arthropods, especially insects, and are comparatively 

 scarce in fishes, from which, however, a few species are known 

 e.g., Glugea stephani of the flounder, G. anomala of the stickleback, 

 etc. Two species are known which are parasitic in gregarines. 

 No species of Microsporidia are known as yet from warm-blooded 

 vertebrates, though their occurrence in such hosts has often been 

 alleged erroneously ; for instance, Leishmania tropica (p. 316), para- 

 site of Oriental Sore, was referred originally to the Microsporidia 

 by Wright (581) under the name Helcosoma tropicum. In addition 

 to Nosema bombycis already mentioned, other highly pathogenic 

 species are known Thelohania contejeani, cause of destructive 

 epidemics amongst river-crayfishes in parts of France ; and Nosema 

 apis, cause of the recent destructive epidemic among hive-bees in 

 England (vide Fantham and Porter, P.Z.S., 1911, p. 625). 



As a general rule the parasites of this order are cell-parasites, 

 which multiply and form their spores within cells, and the trophic 

 phase of the parasite is typically minute and microscopic in size. 

 Usually some particular tissue is attacked, but the pathogenic 

 species owe their lethal powers to the fact that they infest all the 

 tissues of the body. In a few cases, however, the parasites produce 

 cysts of relatively large size, visible to the naked eye in the tissues 

 of the host as, for example, the species of the genus Glugea. 



The most marked effect of the parasites is to produce, in many 

 cases, an extraordinary hypertrophy of the host-cell, and in par- 



