276 THE SPOROZOA 



found infesting Invertebrate hosts, and especially Arthropods. 

 Hence they were termed by Balbiani " psorospermies des Articules." 

 But they have also been found in other classes of animals both 

 Invertebrate and Vertebrate. Glugea laverani, Caull. et Mesn., infests 

 two species of Polychaetes ; an undetermined species of Pleistoplwra 

 has been found by Leger (1897) in a Trematode (Brachycoelium sp.); 

 Glugea Iielminthophthora (Kef.) is found in tapeworms, Taenia spp., 

 and in Nematodes (Ascaris mystax) ; Glugea bryozoides (Korot.), Thel., 

 has been described by Korotneff from the Bryozoan Akyoncellum 

 fungosuin ; while a number of species of Glugea and Pleistoplma are 

 known from various fishes. The range of this sub-order is there- 

 fore wide, and future researches will probably show it to be even 

 more extended than it is known to be at present. 



(b) Habitat, Effects on tJieir Hosts. The Myxosporidia, taken as 

 a whole, seem to be more efficient than any other group of Sporozoa 

 in impairing the health and vitality of their hosts, and are often 

 the cause of the most virulent epidemics. The ravages of the 

 pebrine disease amongst silkworms, caused by Glugea bombycis, is 

 perhaps the most familiar example of their destructive powers, but 

 many other instances could be cited, especially the frequent 

 epidemics amongst fish caused by Myxosporidia both in Europe 

 and America. The destruction wrought by Myxobolus pfeifferi 

 amongst barbel, and by M. cyprini amongst carp, in the rivers of 

 France and Germany, has caused a good deal of attention to be 

 directed to the parasites in question, and in the case of the former, 

 the investigations of Hofer and Doflein elicited some interesting 

 facts. The barbel were found to be infested Avith the Myxobolus in 

 all the rivers of Germany, but while in certain rivers, particularly 

 in the Moselle, the parasite is endowed with powers so deadly that 

 the barbel are killed off in thousands, elsewhere it is comparatively 

 innocuous. The epidemics amongst crayfishes in France, caused by 

 TMlohania contejeani, also deserve special mention. The economic 

 importance of the Myxosporidia has led to their being the object 

 of thorough and extended investigations in recent times. Ten 

 years ago the Myxosporidia were an obscure group of which 

 comparatively little was known ; at the present day, though much 

 remains still to be studied, they are perhaps more thoroughly 

 worked out, and on the whole better understood, than any other 

 section of the Sporozoa. To this result, the careful and laborious 

 researches of Thelohan, Gurley, and Doflein have contributed more 

 especially. 



In the bodies of their hosts the Myxosporidia attack a variety 

 of organs. The PJiaenocystes are typically intercellular parasites, 

 while the Cryptocystes commonly infect cells, but in the former 

 sub-order the trophozoite in its earliest stages may occur either 

 within or between cells (Doflein). The distinction has not, 



