E. Hindle 
157 
forms may be observed. The organism multiplies in the alimentary canal and 
is passed out together with the faeces, thus furnishing a means for the spread 
of the infection from one insect to another. The name Rickettsia trichodectae 
is provisionally given to this parasite, for in spite of the absence of any dis¬ 
tinguishing morphological characters, it can hardly be doubted that it repre¬ 
sents a new species, in view of its occurrence in a distinct host. 
Rickettsia linognathi n. sp. 
The examination of smears from the alimentary canal of the goat louse, 
Linognathus stenopsis, resulted in finding Rickettsia in two examples out of 
57 collected from goats at Cambridge. The parasite does not differ morpho¬ 
logically from the preceding species and as it was only found in smears of the 
contents of the alimentary canal it has not yet been possible to decide whether 
it occurs only in the lumen of the gut, or in addition in the epithelial cells. 
For convenience of reference the name R. linognathi is given to this organism, 
although as in the case of many other bacteria it is impossible to give satis¬ 
factorily distinguishing morphological characters. 
Examination of other Arthropoda. 
In the course of this investigation the gut contents of many species of 
blood-sucking insects, lice, Mallophaga and fleas have been examined and it 
is noteworthy how remarkably free from bacteria is the alimentary canal of 
most of these insects. Occasionally rod-shaped bacilli and sarcina like bodies 
were found, especially in the films made from lice, but as a rule they were 
absent. 
In the case of Haemotopinus suis from the pig, most of the films were 
found to contain irregular-shaped bodies resembling the symbiotic fungi 
which occur in various species of insects, and especially in Hemiptera (Buchner, 
1912). 
Discussion of results. 
Up to the present time nine species of Rickettsia have been recorded in 
addition to Dermacentroxenus rickettsia Wolbach (1918) which probably be¬ 
longs to the same group of organisms. These different species and their habitats 
are summarised in the following table: 
Rickettsia prowazelci da Rocha Lima 1916. Occurs in the lumen of the intestine and tlie 
epithelium of the mid-gut of Pediculus humanus and in the blood and organs of typhus 
patients. 
R. quintana da Rocha Lima 1916. Occurs in the lumen of the alimentary canal of 
Pediculus humanus and in the blood and organs of trench fever patients. 
R. pediculi da Rocha Lima 1917. Occurs in the lumen of the alimentary canal of Pedicu- 
lus humanus. 
R. melophagi Noiler 1917. Occurs in the lumen of the alimentary canal and the ovaries 
of Melophagus ovinus. 
R. ctenocephali Sikora 1918. Occurs in the alimentary canal of Ctenocephalus canis. 
