(136) 



STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-FLY. 377 



parasitic in the gut of Nepa cinerea, from which figures it 

 may be understood how the mistake lias arisen. Through, 

 this misinterpretation Prowazek was led to consider that the 

 parasite 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 difficulty, 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. muscae-domesticse 

 into three stages the preflagellate, 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 preflagellate stage, which Patton (1909) describes, 

 usually occurs in the masses which lie within the peritrophic 

 membrane. 1 They are round or slightly oval bodies (I), their 

 average breadth being 5'5 /a. The protoplasm is granular and 



1 I assume that Patton refers to this membrane by the term " peri- 

 tricheal membrane." 



