HYDRA AND MOSQUITO LARVA 161 
transmission of the organism of yellow fever. These are discussed in our 
section on yellow fever. 
Various flagellate Protozoa have been reported as parasites of mosquitoes. 
These forms do not require an intermediate host. They may be transmitted 
hereditarily by breaking through the digestive tract and, invading the body- 
cavity, entering the eggs of the insect. One of these forms has been described 
by Léger as Crithidia fasciculata, as an intestinal parasite in Anopheles maculi- 
pennis in France. Novy, MacNeal and Torrey report the same form from Culex 
in Michigan. The brothers Sergent have described a form of Herpetomonas 
(H. algeriense) from females of Culex pipiens and Aédes calopus. Ronald 
Ross, Chatterjee, Léger, Patton and Stephens and Christophers have found 
similar parasites in mosquitoes. A form described by Novy, MacNeal and 
Torrey from various mosquitoes occurring about Ann Arbor, Michigan, as 
Trypanosoma. culicis is now referred to the same genus. There appears to be 
some reason to believe that the genera Herpetomonas and Crithidia represent 
merely different phases of the same organisms and that the same forms have been 
described in both genera. 
Giles, in India, found a stalked infusorian attached in numbers to mosquito 
larvee. In the second edition of his “ Gnats or Mosquitoes,” p. 151, he says: 
“T have repeatedly found every Jarva in a pool simply covered by these para- 
sites, which lie crowded together in enormous numbers, attaching themselves 
especially to the softer parts of the integments, such as the angles between the 
anal tubercles, and the soft membranes between the segments. Larve affected 
in this way have a peculiar, slimy appearance, and seldom appear healthy, 
though it is difficult to see how these ecto-parasites can be harmful, unless it 
may be that being, at the very least, greedy mess-mates, they may appropriate to 
themselves an undue share of the food that would otherwise fall to the share of 
their hosts. Nevertheless, I strongly suspect that they may be the cause of the 
inexplicable disappearance of larve, already alluded to, from situations where 
they were just before present in abundance.” 
Vorticellids have also been often found upon mosquito larve in this country. 
H. P. Johnson, in an appendix to Smith’s report for 1902, states that he fre- 
quently found beautiful clusters of these creatures on the thorax, abdomen, and 
even the head of the larve of Culex pipiens. He states that they may be so 
abundant as to give the thorax especially a whitish gelatinous appearance to the 
naked eye. He believes that it is unlikely that these vorticellids do the larve 
any harm, and that the latter simply afford them an attachment and transpor- 
tation ; possibly also food, brought by the vortex which the mosquito larva creates 
in the water. In fact vorticelle are very common on larve in open pools. The 
only harm we ever saw done by them was in the case of an Anopheles larva 
observed by one of us (Dyar) ; this was so loaded with Vorticella that it could 
not turn its head to feed properly and eventually died. 
OTHER LOWER ANIMALS. 
The common fresh-water hydras (Hydra viridis and Hydra fusca) will de- 
stroy mosquito larve that come within reach of their tentacles. One of us 
