A. Porter 
359 
hereditary infection, which is actually attained in C. melophagia, where 
the Crithidia are found within the eggs and embryo of the Melophagus. 
There is undoubted evidence that the Gerris becomes infected with 
Crithidia when the bugs are very young. Very small forms, the 
youngest nymphs obtainable, have been found to be parasitised, but 
this is explicable other than by hereditary infection. 
The breeding grounds of the Gerris are quiet and sheltered spots, 
and defaecation follows oviposition very commonly. The young larva 
then is hatched in contact with faeces, some of which may be infected, 
and in its early quest of food, some of the crithidian cysts are doubtless 
ingested with the liquid taken up from the leaves, etc. around the 
young insect. 
General Remarks. 
The genus Crithidia was founded by Leger (1902) for a flagellate 
that he found in Anopheles maculipennis. Two forms of the parasite 
were described by Leger ; one consisted of a short, truncated body with 
a small flagellum, while the other possessed the usual long, tapering 
body, drawn out at its anterior end into the long flagellum, to which it 
was connected by a narrow, undulating membrane. From a study of 
the short, oval forms, Leger named the parasite Crithidia fasciculata, 
the name Crithidia denoting an oat. These short, oat-like forms would 
now be described as the late pre-flagellate stages of the parasite, and in 
this condition they are much like those of Herpetomonas. The study 
of the complete life-history of the parasites is necessary to determine 
fully to what genus any young form may belong. 
Prowazek (1904) gave a life-history of a parasite, Herpetomonas 
muscae domesticae from the housefly, and stated that this organism had 
two flagella, a statement that has not been generally accepted. For 
some reason, the appearance of this memoir has caused much confusion 
of the genera Herpetomonas and Crithidia. 
Lithe (1906) retains both genera, characterising Crithidia as possess¬ 
ing an undulating membrane and single flagellum, Herpetomonas as 
having no membrane but a long flagellum. 
Novy, MacNeal and Torrey (1907) believe that Leger was dealing 
with a mixed infection of Herpetomonas and Crithidia in Anopheles 
maculipennis, which is quite possible ; but these investigators character¬ 
ise Herpetomonas as being the organism with the undulating membrane, 
their view therefore bemg quite opposed to that of all other workers on 
these organisms. 
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