A. Porter 
363 
membrane follows, and then that of the body. The daughter halves 
gradually diverge and finally separate. In pre-flagellate division, rosettes 
may be formed by several rapid, repeated, longitudinal divisions 
(Fig. 20). The fully flagellated individuals first divide into two 
and repeated division may result in rosettes, but these very rapidly 
break up. Aggregation rosettes of mature flagellates are, however, 
extremely common (Fig. 47). 
(10) The mode of infection is a casual one, the young nymphs 
taking up faeces containing crithidian cysts from the leaves of water 
plants. 
(11) The parasite is purely a parasite of insects, occurring iu two 
species of Gems, G. fossarum and G. paludum. The systematic 
position of the parasite is near the Trypanosomes in the family Trypa- 
nosomatidae. 
(12) There is much variation of form exhibited by the adult 
flagellate. Some of the very long parasites (PI. IV, Figs. 39, 44—46). 
appear to be peculiar to the Crithidia found in the gut of G. paludum, 
and have not been figured before so far as I know. This polymorphism 
needs careful attention, and is very confusing if only isolated stages of 
the parasite are studied. A similar remark applies to other crithidial 
and herpetomonad forms. 
REFERENCES. 
The principal papers relating more especially to the genus Crithidia are set forth 
in the following list. Further references will be found in some of the papers cited. 
Flu, P. C. (1908). Tiber die Flagellaten im Darm von Melophagus ovinus. Archiv 
f. Protistenkunde, xii. pp. 147— 153, 1 plate. 
Legkr, L. (1902). Sur un flagelle parasite de 1’ Anopheles maculipennis. C. R. Soc. 
Biol., Liv. pp. 354—356, 10 figs. 
Moore, J. E. S. and Breinl, A. (1907). The Cytology of the Trypanosomes. Ann. 
Prop. Med. and Parasitol., I. pp. 441—480, 5 plates. 
Novy, F. G., NacNeal, W. J. and Torrey, H. N. (1907). The Trypanosomes of 
Mosquitoes and other Insects. Journ. Pnfect. Diseases, iv. pp. 223—276, 
7 plates. 
Patton, W. S. (1908). The Life-Cycle of a species of Crithidia parasitic in the 
intestinal tract of- Gerris fossarum, Fabr. Archiv f. Protistenkunde, xii. 
pp. 131—146, 1 plate. 
- (1909). The Life-Cycle of a species of Crithidia parasitic in the intestinal 
tracts of Tabanus hilarius and Tabanus sp. Archiv f. Protistenkunde, xv. 
pp. 333—362. 
