HYDRA AND MOSQUITO LARV^ 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 Leger as Crithidia jasciculata, as an intestinal parasite in Anopheles maculir 

 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 Aedes calopus. Eonald 

 Ross, Chatterjee, Leger, Patton and Stephens and Christophers have found 

 similar parasites in mosquitoes. A form described by ^0;% 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 

 larvge. In the second edition of his " Gnats or Mosquitoes," p. 151, he says : 



" I have repeatedly found every larva 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. Larvse 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. Kevertheless, I strongly suspect that they may be the cause of the 

 inexplicable disappearance of larvae, already alluded to, from situations where 

 they were just before present in abundance." 



Vorticellids have also been often found upon mosquito larvae 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 larvas 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 larvae 

 any harm, and that the latter simply afford them an attacliment and transpor- 

 tation ; possibly also food, brought by the vortex which the mosquito larva creates 

 in the water. In fact vorticella? are very common on larvae in open pools. The 

 only hann 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 fu^^ca) will de- 

 stroy mosquito larvae that come within reach of their tentacles. One of us 



