STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-FLY. 375 
dome Stic 00 described by Burnett and the Cercomonas 
in use arum of Leidy. For this form figured by Stein, a new 
genus, Herpetomonas, was instituted by Kent (1880-81), 
and it is taken as the type-species. It was not until the 
economic importance of certain of the haemo-flagellates was 
recognised that other flagellates, including H. musem- 
domesticae, received further attention, and then Prowazek 
(1904) described with great detail the development of this 
species. In the previous year Leger (1903) had given a short 
account of it, and since Prowazek’s memoir Patton (1908, 
1909) has given short preliminary accounts of his study of 
the life-history. The accounts of both these authors differ in 
several respects from that of Prowazek, as will be shown. I 
have examined a very large number of the contents of English 
specimens of M. domes tica, but, with one or two doubtful 
exceptions, unfortunately I have been unable so far to 
discover any of these flagellates in my film preparations. 
The full-grown flagellate (VIII) measures 30-50 g in 
length. The body is flattened and lancet-shaped, the pos- 
terior end being pointed and the anterior end bluntly rounded. 
The alveolar endoplasm contains two nuclear structures. In 
the centre is the large “ trophonucleus ” {tr.) •, it contains 
granules of chromatin, but is sometimes difllcult to see. Near 
the anterior end the deeply staining rod-shaped “ kineto- 
nucleus” (blepharoplast of many authors) (/c.) lies, usually in 
a transverse position. The single stout flagellum, which is a 
little longer than the body of the flagellate, arises from the 
anterior end, near the kinetonucleus. Prowazek describes the 
flagellum as being of a double nature and having a double 
origin ; this, which is a mistaken interpretation, is repeated 
by Lingard and Jennings (1906). 
fi'his mistake, as pointed out by Leger and Patton, is due to 
the fact that the majority of the adult flagellates have the 
appearance of a double flagellum, which represents the 
beginning of the longitudinal division of the flagellate (VI). 
Patton (1908) figures a stage in H. lygaei with the double 
flagellum, and Leger (1902) in a similar .stage in H. jaculum, 
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