E. Kindle 
129 
Kent’s (1881) diagnosis of the genus is as follows : 
“ Animalcules free-swimming, elongate or vermicular, highly flexible ; 
the posterior extremity often the most attenuate, but not constituting 
a distinct caudal appendage; flagellum single, terminal; contractile 
vesicle usually conspicuous. Habits mostly endoparasitic ” (Vol. l, 
p. 245). 
However, two pages before this {loc. ciL, p. 243), Kent had already 
given the diagnosis of another new genus, Leptomonas, formed for the 
reception of a flagellate parasite occurring in the intestine of Trilobus 
gracilis, and which had been described and figured five years previously 
by Blitschli (1876). 
The diagnosis of the genus Leptomonas was given as follows: 
“Animalcules free-swimming, persistent in shape, elongate fusiform 
or aciculate, bearing a single long undulating flagellum at the anterior 
extremity; no distinct oral aperture yet detected.” 
The only species referred to the genus was L. biitschlii Kent. 
If the respective diagnoses of the genera Heiyetomonas and Lepto- 
monas are compared it will be seen that the differences between them 
are extremely difficult to recognize at the present time. The presence 
of a contractile vacuole and the extreme flexibility of the body in 
Herpetomonas constitute the only distinct differences between the two, 
and neither of these characters is recognized in any modern definition 
of the genus. The contractile vacuole is not present in Herpetomonas 
7nuscae-domesticae, nor in any other member of the group, and yet this 
constitutes the main point of distinction between the above two genera. 
As for the flexibility of the body, this is a very uncertain character and 
is insufficient to distinguish two genera. 
On these grounds, therefore, Leptomonas Kent and Herpetomonas 
Kent should be united and become one genus. 
This fact was recognized by Butschli (1884) but instead of retaining 
the name Leptomonas that of Herpetomonas was selected, and the former 
became a synonym. According to the “ Law of priority ” in the 
Internatio7ial Code of Zoological Nomenclature the genus Leptomonas, 
being described two pages before Herpetomonas, has priority and therefore 
should have been retained. 
Still further confusion was caused by Senn (1900) who removed 
Herpetomonas muscae-domesticae to the genus Leptomonas. 
The latter therefore was represented by two species, muscae-domesticae 
and biitschlii. The genus Herpetomonas was retained for the reception 
of the rat trypanosome, described by Kent (1881) as Herpetomonas 
Parasitology v 
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