1911.] 



Parasitic in Pediculus vestimenti. 



515 



fair number of those adults that died did so within a short time after a 

 meal, their alimentary canals containing much unchanged blood. 



Regarding the specific name of the body-louse there is much uncertainty. 

 Neumann, in a recent paper (July, 1911), suggests that P. vestimenti is a 

 sub-species of P. capitis, and would then be called P. capitis vestimenti. 

 However, a discussion of such a difficult matter of nomenclature is quite 

 outside the scope of this paper. 



Summary and Conclusions. 



1. Herpetomonas pediculi is a parasite of the body louse, Pediculus vestimenti. 

 The parasite appears to be confined to the alimentary tract and faeces of its 

 host (adult and larva), one phase of it having been recovered from the 

 dejecta. The parasite is spread from louse to louse by the contaminative 

 method, cysts of the parasite being swallowed by the insect. The whole life- 

 cycle has been followed in the living material. 



2. Movements of the flagellate are very rapid and somewhat spasmodic, and 

 are easily accomplished by the aid of the flagellum. Rotatory motion and 

 movements of flexion occur. 



3. The parasite exhibits three well-marked developmental phases, united 

 by a continuous series of intermediate forms : — (i) The pre-flagellate, which 

 produces a flagellum and elongates (figs. 1 — 7), and becomes (ii) the 

 flagellate (figs. 8 — 18), which, after a growing and multiplicative phase by 

 longitudinal fission (figs. 19 — 21), forms (iii) the resting, " encysted " post- 

 flagellate form, adapted for extra-corporeal life (figs. 22 — 29). 



4. Pre-flagellate stages, best found in the oesophagus and proventriculus of 

 the louse, or in the larva, strongly resemble Leishman-Donovan bodies. 

 They are 6 fx, to 7 /x long and 4 /x to 5 fi broad. The nucleus and blepharo- 

 plast are well defined. A chromatophile area, from which the flagellum 

 develops, is present. 



5. The flagellate forms occur chiefly in the mid-gut. The body length is 

 from 11 fi to 26 /x in those I have examined. The cytoplasm is finely 

 alveolar. The nucleus is round or oval, and the blepharoplast stains deeply. 

 Aggregation rosettes of flagellates of various ages and sizes are occasionally 

 found (fig. 13). 



6. Post-flagellate forms are oval, usually provided with a " skin-tight " cyst. 

 The blepharoplast seems smaller than that of the flagellate or pre-flagellate. 

 This stage is best observed in the rectum of the louse and can be recovered 

 from the faeces. 



Radially striated, thick-walled cysts occur very rarely (fig. 29). 



7. My experiments show that H. pedicidi is not a stage of a vertebrate 

 VOL. lxxxiv. — b. 2 p 



