1911.] 



Parasitic in Pediculus vestimenti. 



51 1 



near the blepharoplast, and occasionally a minute basal granule can be 

 distinguished with difficulty. 



Aggregation rosettes. — Just as division rosettes are infrequent, so aggrega- 

 tion rosettes or clusters are uncommon. It is noteworthy that the members 

 of an aggregation rosette (fig. 13) may be of different sizes and ages. In 

 such rosettes, the parasites either mass themselves around some food particle 

 with which they are in contact by their flagella, or else several organisms 

 intertwine their flagella and so form a sort of bouquet or ball of living 

 organisms, all vibrating slowly from a common centre provided by their 

 interlaced flagella. These rosettes in time break up into the component 

 units. One after another, the slow-moving organisms manage to detach 

 themselves and swim away until the last two separate. The object under- 

 lying these simple rosette formations is not fully understood. Possibly it 

 enables the flagellates to withstand better any currents in the gut, and so 

 gives them a somewhat longer lease of life as flagellates, before encystment 

 overtakes them. 



0. The Post-flagellatc Stage. 

 The post-flagellate stages of H. pediculi (figs. 25-29) when fully formed 

 are small bodies (less than the pre-flagellates) containing protoplasm and 

 a nucleus, to which the blepharoplast may be apposed, or in which nucleus 

 and blepharoplast can be distinguished as separate entities. The blepharo- 

 plast is often somewhat smaller than in the other phases of the parasite. 

 The cyst wall is extremely thin, staining pinkish after Giemsa (figs. 27, 28). 

 The blepharoplast is not always easy to demonstrate in stained preparations, 

 but that it must be present is obvious when one has taken the trouble to 

 watch the process of post-flagellate formation in the living animal and has 

 studied a series of stained preparations of intermediate forms (figs. 22-26). 

 Cysts with thick, radially striated walls (fig. 29) have very rarely been 

 encountered, and I am inclined to think that the presence of the swollen 

 gelatinous wall containing striations and enclosing a parasite with chromatoid 

 granules is a sign of degeneration. 



Herpetomonas pediculi is A Natural Parasite of Pediculus vestimenti. 



Eecently much controversy has arisen from statements made to the effect 

 that flagellates found in sanguivorous insects must be regarded as develop- 

 mental stages of trypanosomes. Accordingly — ignoring the evidence of life- 

 cycle and morphology- — IT. pediculi would be regarded by some as a phase of a 

 trypanosome. Sweeping statements such as that quoted are rarely logical, 

 and when they are based upon a series of speculations and single instances 

 instead of on an accumulation of facts, they are usually unsound. 



