STRUCTUEE, DEVELOPMENT, AND BIONOMICS OF HOUSE-FLY. 377 
parasitic in the gut of Nepa cinerea, from which figures it 
may be understood how the mistake has arisen. Through 
this misinterpretation Prowazek was led to consider that the 
pai’asite was of a bipolar type, in which the body had been 
doubled on itself so that the two ends came together and the 
flagellum remained distinct. The flagellum, according to 
Leger, is continued into the cytoplasm as a thin thread, 
which stains with diflBculty, and terminates in a double 
granule above the kinetonucleus ; this double granule is no 
doubt the “diplosome” of Prowazek. According to the 
latter author another deeply staining’ double thread {s.t.), 
that appears to be spirally coiled, runs backwards from the 
kinetonucleus and terminates posteriorly in a distinct granule, 
shown in fig. VIII. 
The flagellates congregate in the proventriculus or in the 
posterior region of the intestine, where they become united 
by their anterior ends to form rosettes. Prowazek states that 
in the rosette condition the living portion of the flagellate 
resides, as it were, in the long tail-like process. 
Patton divides the life-cycle of H. muscte-domesticte 
into three stages — the prefiagellate, flagellate, and post- 
flagellate. The last two are common, but the first stage is 
not common, and Prowazek appears to have overlooked it. 
For convenience I have described the flagellate stage first, 
and the process of division in this stage is simple longitudinal 
fusion. The nuclei divide independently, and the kineto- 
nucleus usually precedes the trophonucleus. The latter 
undergoes a primitive type of mitosis, in which Prowazek 
recognised eight chrosomes (VII). The flagellum divides 
longitudinally, and each of the two halves of the kineto- 
nucleus appropriates one of the halves with its basal granule. 
The prefiagellate stage, which Patton (1909) describes, 
usually occurs in the masses which lie within the peritrophic 
membrane.^ They are round or slightly oval bodies (I), their 
average breadth being 5’5 p. The protoplasm is granular and 
* I assume that Patton refers to this membrane by the term “ peri- 
tricheal membrane.” 
