302 ILLINOIS ACADEMY OF SCIENCE 



Twenty-two larvae were kept in the laboratory, and meta- 

 morphosed into pupae and adults. Thirteen pupae and 

 nine adults were examined. In one adult were seen a 

 few spores in fresh smears. Careful examination of 

 numrous sections of larvae failed to reveal the slight 

 infection whatsoever. This may be interpreted as indi- 

 cating that the larvae became infected either when they 

 were very young or when they swallowed a large amount 

 of infected tissue of the larva dead from the infection 

 and underwent decaying at the bottom of the pool where 

 they were found, so that the heavy infection resulted in 

 a comparatively short time. 



The infected larvae were more whitish opaque in color 

 than normal, with more or less distended thorax. Yet 

 they were as active as normal ones. However, they died 

 more rapidly than majority in the laboratory. Although 

 there has been one case of ambiguous slight infection in 

 an adult, the parasites seem to exercise a fatal effect 

 upon the host, and the larvae once infected, perish with- 

 out completing their life cycle. 



This is the second Microsporidian found parasitic in 

 the dipterous insects under discussion, although there 

 have been some doubtful cases which did not furnish the 

 necessary proof to show their belonging to Microsporidia. 

 The first microsporidian parasite of mosquitoes was de- 

 scribed by Hesse in 1904 from France, who noticed a few 

 larvae of Anopheles maculipennis infected by Thelo- 

 hania legeri Hesse. The seat of infection was adipose 

 tissue as in the American form. Hesse however states 

 that the infection was rare and the infected larvae did 

 not seem to suffer at all from the parasites. 



In two out of twelve larvae of Anopheles punctipennis 

 examined, another Microsporidian was noted to occur in 

 the adipose tissue. The small number of specimens and 

 the smear preparation do not allow the writer to report 

 the details as the observation is still incomplete. The 

 effect of the parasite upon the host also remains to be de- 

 termined in future. 



In nine out of thirty nymphs of Baetis sp. (?). ex- 

 amined, third Microsporidian was found to occur exclu- 



