290 H. M. WOODCOCK. 



Mammalian Forms. 



(a) Non-pathogenic. — T. lewisi, (Kent), 1879. (Syn. Herpeto- 

 monas 1., Kent.) Length 24-25 fi, breadth 14-lf /x.' This species (figs. 16 A, 

 27) is characterised by its thin, drawn out, and pointed anterior extremity, 

 and also by the position of the trophonucleus in the posterior half or third of 

 the body. The cytoplasm is very clear and free from grannies. Hosts : (V.) 

 Mus decumanus, M. rattns, and M. rufescens; (I.) the life-cycle can 

 certainly be undergone in the rat-louse, Haematopinus spinulosus, which 

 is therefore a true alternate host. Prowazek thinks, however, that fleas 

 may also serve the purpose of transmission. A closely allied species (by 

 some considered as only a race or variety of T.lewisi) is found in Cricetus 

 arvalis (f rumentarius?), the hamster; this form is not inoculable into 

 rats, and, conversely, T. lewisi is not capable of living in the hamster. 



T. duttoni,- Thiroux, 1905. Length 25— 30/t, of free flagellum 6| — 

 10 /i ; breadth 2|jn. This parasite resembles T. lewisi, and also, in a general 

 fashion, the Trypanosomes of other small Rodents mentioned below. 

 (V.) host: Mus musculus. This form is not inoculable into rats, and is 

 therefore distinct from T. lewisi. It was found in mica in Senegal, and 

 Thiroux wonders whether it is identical with the parasite described as a 

 Herpetomonad by Button and Todd (21), also from Senegambian mice. 

 In the latter, however, no undulating membrane was observed, and hence 

 it is doubtful whether it was really a Trypanosome. 



In addition to the above forms, Trypanosomes have been casually observed 

 in various other Rodents, but as yet they are unnamed and not much is 

 known about them. 



Petrie (82) recently found three rabbits spontaneously infected with a 

 Trypanosome (fig. 43 a). Tlie parasites were quite numerous in the blood, 

 and, in one case, present for six months at least, without causing any ill- 

 effects. This form appears to be similar, as regards size and morphology, 

 to T. lewisi, but most likely belongs to a distinct species, since the latter 

 form is not inoculable to rabbits. 



Another Trypanosome (fig. 43 b) has been recently observed by Donovan 

 in an Indian squirrel (Sciurus palmarum). Its total length was 18 — 20/<, 



• The dimensions given are intended to indicate the average size of the 

 adult parasite, but, as above said, they can only be considered approximate. 

 Unless otherwise stated, the length is inclusive of the flagellum. 



' The writer commenced this article with the intention of having a 

 figure of every species ; tlie number of those known has increased so 

 greatly, however, while it has been in progress, that this has proved 

 impracticable, and hence some of the most recently described species are 

 unfieured. 



