1911.] 



Parasitic in Pediculus vestimenti. 



509 



flagellar end is continuous, and by the time that the flagellum has reached 

 its full length the non-flagellar (or posterior) end has elongated and become 

 fully developed. 



During the actual flagellate stage (figs. 8-18) little in the way of actual 

 development occurs, but the vital activities of the organism are displayed by 

 vigorous multiplication. Increase in numbers in H. pediculi takes place by 

 longitudinal division. The parasites about to divide seem to grow broader 

 just prior to the act and to become more granular. The first indication of 

 division is shown by tbe concentration of the substance of the blepharoplast 

 into two masses which are connected together by a very narrow neck. The 

 dumb-bell like body so formed (fig. 19) gradually separates into two distinct 

 blepharoplasts, placed slightly obliquely, one on either side of the body 

 (fig. 20). The intra-eellular part of the flagellum (or rhizoplast) commences 

 to divide just after the blepharoplast, and the split appears to extend 

 forwards. Concentration of the nuclear material occurs simultaneously, and 

 the nucleus becomes constricted, usually in the median line and parallel to 

 the long axis of the body, but occasionally markedly to one side. The 

 constriction deepens, and ultimately two nuclei are produced. These migrate 

 to the sides of the organism, and fission of the general cytoplasm commences 

 (figs. 20, 21). The flagella lash about very much at this time, and their 

 vigorous action aids in the separation of the daughter organisms. The 

 latter gradually diverge until they come to lie in a straight line, and finally 

 become separated from one another at the apex. The fission is practically 

 always followed by active swimming movements of the daughter organisms. 

 Consequent on this great activity of the daughter forms immediately after 

 division, rosettes of Herpetomonads, due to repeated longitudinal division 

 and non-separation of the resultant parasites, are exceptional. Division 

 is best seen in the mid-gut of the louse. 



After a series of longitudinal divisions, resulting in the production of a 

 number of flagellate individuals, a reaction sets in, and the parasite prepares 

 for life outside the body of its host. As the Herpetomonad passes back- 

 wards into the very dark semi-digested blood in the hind gut of the louse, 

 the chromatin of its flagellum dwindles, and appears to be absorbed 

 (figs. 22-25). The cytoplasm concentrates around the nucleus, to which 

 the blepharoplast also is drawn nearer. The parasite becomes more or less 

 rounded or oval, and proceeds to secrete a thin, gelatinous wall, which 

 rapidly hardens to a " skin-tight " coat around the organism, which, in this 

 sense, may be said to encyst (figs. 26-28). Thus prepared and protected, the 

 oval bodies, now known as post-flagellates, pass from the gut of the host, mingled 

 with the dejecta to recommence the life-cycle if ingested by a new host. 



