MICROSPORIDIA^ — PARASITIC IN MOSQUITOES 171 



mechanical pressure or perhydrol and staining with Loffler's or 

 Fontana's mixtures, proved that the fully extruded filament was 

 57 to 72m long, sometimes reaching 98m, and at the same time 

 proved that Stempell's calculation of the number of turns of the 

 coiled filament was not correct. 



Hesse caused the extrusion of the filament in Thelohania legeri 

 by means of iodine water, and found it to be about 50^ long, 

 while the present writer used the pressure and staining method 

 for the present parasite. This has been recognized as a reliable 

 way of studying the filament, especially in Microsporidia and is 

 accepted by some workers, as Erdmann ('17). Consequently, 

 the difference in length of the filaments in the two species under 

 discussion cannot be used as a basis of distinction. 



Yet the rather conspicuous difference in size of the spores pre- 

 vents the writer from assuming these two forms as identical, 

 especially as Hesse mentioned an irregularity of the dimensions, 

 which is not the case in the American form. Hesse states that 

 the spores of Thelohania legeri measure generally 8^ by 4/i, that 

 in certain sporonts they measure only 6m by 3m, and in some mac- 

 rospores 12m by 5m. The spores of American species are uni- 

 formly much smaller, being 4.75 to 6m by 3 to 4m, without any 

 dimorphism or regular abnormality of the spore. 



Hence, the writer thinks that the species under consideration is 

 not identical with the closely allied Thelohania legeri Hesse, and 

 is a new form which has not been recorded before. He, there- 

 fore, names it Thelohania illinoisensis. 



NOSEMA BAETIS NOV. SPEC, PARASITIC IN BAETIS SP.(?)2 



Forty-two nymphs of Baetis sp. (?) w^ere collected in the drain- 

 age ditch at Urbana, Illinois, on September 25, October 3, and 

 November 17, 1919, and were kept in an aquarium in the labor- 

 atory. Six out of twenty-four nymphs collected on the first 

 two dates and two out of eighteen of the last collection were in- 

 fected by a Microsporidian, for which the name Nosema baetis 

 nov. spec, is proposed. 



2 The writer is indebted to Mr. J. R. Malloch, of the Illinois Natural History 

 Survey, for the generic identification of the insect. 



