172 R. KUDO 



The parasites attack the adipose cells, all other tissues remain- 

 ing uninfected. The thorax of the infected nymph was strik- 

 ingly whitish opaque, and was more or less distended, compared 

 with that of normal individuals. Although the normal insects 

 swam away very rapidly from anything put into the water, the 

 infected ones showing the above-mentioned external characters, 

 were caught easily by means of forceps. The decrease in activity 

 of the host insect is undoubtedly due to the decrease of muscular 

 activity, which relation is discussed elsewhere (p. 176). 



As the number of these insects was small, while on the other 

 hand, a large number of newly hatched larvae of Culex pipiens 

 was available, the latter were used for artificial infection. A 

 number of three-day-old larvae of Culex pipiens were reared in 

 an aquarium which was filled with water suspension of the micro- 

 sporidian, made from an infected Baetis nymph. The larvae 

 seemed to eat willingly the small fragments of the infected tissue. 

 Four larvae were fixed daily until the tenth day, none dying dur- 

 ing this period. The examination of sections of these experi- 

 mental larvae failed to reveal any infection whatsoever. Abun- 

 dant spores which were found in the alimentary tract of the larvae 

 did not show any recognizable changes in their internal structure. 

 From this experiment it may be stated that Nosema baetis does 

 not infect three-day-old larvae of Culex pipiens in the laboratory. 



The following observations on its schizogony and sporogony 

 have been carried out in smears and section preparations of 

 naturally infected Baetis nymph. 



The youngest intracellular stage, the schizont, was found in the 

 adipose cell. It is a small rounded body about Sfx in diameter, 

 and contains a comparatively large nucleus, surrounded by a 

 clear and narrow space (fig. 75). In general appearance it re- 

 sembles Nosema bombycis (Kudo, '16). The protoplasm is 

 densely granulated, staining bright blue with Giemsa. The 

 schizont multiplies by binary fission. The nuclear division 

 seems to be amitotic^ the nucleus simply divides into two parts, 

 at first separated by a narrow space (figs. 76, 77) ; later these two 

 portions move toward the opposite poles, often showing an arch 

 shape (figs. 76 to 93). The daughter schizonts repeat the divi- 

 sion until the host cell becomes filled with the sporonts. 



