D. L. Mackinnon 
29 
(Leger and Duboscq, 1909); and I believe that the same spirochaete 
will be found in other aquatic insect larvae in the future. 
Observations such as these lead one to protest against the present 
tendency to regard each new parasite as peculiar to one host—a 
tendency which leads to the frequent formation of new species on 
insufficient grounds, and is surely opposed to the principles of common- 
sense. 
On two or three occasions I saw some small amoebae in the hind-gut 
of the caddis-worm. The amoebae were very few in numbei’, and I 
never obtained any satisfactory stained preparations. I shall content 
myself here with some brief observations made on the living organisms. 
Material and Methods. 
The caddis-Hies and their larvae and pupae were collected in the 
neighbourhood of Aberdeen at various times from April 1909 till 
November 1910. Larvae from ponds near Dundee were found to be 
similarly infected. The infected individuals belonged mainly to the 
genera Limnophilus and Anaholia. 
The microsporidian occurred in the fat-body of the larva: with this 
exception, the parasites were all found in the hind-gut along with the 
trichomonad. I saw no trace of them in the upper regions of the 
alimentary tract, 
I attach prime importance to the study of the living parasites. 
This can be done either by observing them as they move about within 
the transparent gut of the young larva, or in teased-out preparations of 
the gut contents under a waxed-down coverslip. 
Examination in soda solution of material that had been fixed in 
osmic vapour (Schewiakoff’s method) was found useful for determining 
the number of flagella, and their point of origin. 
For permanent preparations, fixation with sublimate alcohol (Schau- 
dinn’s formula) and staining with Heidenhain’s iron-haematoxylin gave 
the best results in the case of the flagellates. Attempts to stain 
Embadomonas by the modified haematoxylin method used by Rosen- 
busch for trypanosomes (Arch. f. Protistenk. xv. 1909, p. 263) proved 
unsuccessful. 
The microsporidian was first smeared, and then fixed and stained 
variously ; but better results were got by fixing the infected larva 
whole, and cutting sections^of it : portions of these sections were quite 
thin enough to display the individual spores. Fixation with sublimate 
