246 
New Protist Parasites 
similar to T. caviae : it is not impossible that some ill-defined species of 
Monocercomonas , Grassi, parasitic in insect larvae, may belong here. 
At any rate, I am about to describe a typical trichomastix, which occurs 
regularly and in fairly large numbers in the aquatic larvae of certain 
trichopterids—the so-called “ caddis-worms ” of our ponds and streams. 
Looking to the habitat of the hosts, I was at first inclined to think 
that there might be some connection between the trichomastix of frogs 
and toads, and that of the larval insect. The caddis-worm might easily 
swallow the cysts of T. batrachorum in the course of feeding, and might 
provide a suitable field for development of that flagellate. The chances, 
however, are against this— i.e. other insect larvae feeding alongside the 
caddis-worms never showed any infection with trichomonads: then 
again, Trichomonas batrachorum, Perty, which is much the commoner 
trichomonad in frogs, has no counterpart among the parasites of the 
insect: lastly, though it is difficult to define the different species of 
Trichomastix, yet I hope to be able to show that the parasite of the 
trichopterid larva has certain minor features that help to separate it 
morphologically from hitherto-described species, and justify my calling 
it Trichomastix trichopterae, n. sp. 
II. Material and Methods. 
The larval iusects were collected from ponds and streams in the 
neighbourhood of Aberdeen at various times from April until the end of 
December, 1909. Specimens from different localities were found to be 
equally infected. 
The forms examined included species of Limnophilus ( L. rhombicus, 
L., and L. flavicornis, L.), Anabolia, Stenophylax, Sericostoma, and 
Mystacides. 
The species of Limnophilus were always the most richly infected, 
Stenophylax and Sericostoma much more slight^, and Mystacides never 
showed any infection. This probably has reference to the feeding- 
grounds of the hosts, and the resulting degree of suitability of the 
intestinal contents to the needs of the parasites. For instance, 
Limnophilus, living in stagnant waters, swallows large quantities of 
bacteria, which multiply extensively in the hind part of the gut, and 
form excellent pabulum for the flagellates. Anabolia, Stenophylax, and 
Sericostoma I found mainly in streams, where they feed more “ cleanly,” 
and are not nearly so much infected with bacteria. Mystacides occurred 
in slowly running water, where, judging fi’om its intestinal contents, it 
