FILAEIA SANGUINIS HOMINIS IN THE MOSQUITO. 371 



deposited on the surface of water, do not keep together in a hoat-shaped cluster, as do 

 those of the true Filaria mosquito, hut float about separately, tending to adhere to the 

 sides of the bottle. There is no danger of confounding this species with the true Filaria 

 mosquito. The other species of tiger mosquito is smaller, and in this way is liable to 

 be mistaken for the Filaria mosquito ; but a close inspection shows it to be smaller in 

 size and darker in colour than the true species ; and, in addition to these points of 

 distinction, the little flecks of white and white bands on legs and body serve, with a 

 little care, to prevent mistake. I have often found the Filaria in the blood in the 

 abdomen of both of these mosquitoes, but never in such numbers as one finds them in 

 the true Filaria mosquito. In the thorax I have found them slightly advanced in 

 development in the larger tiger mosquito ; but although I have examined a considerable 

 number of this species on the third day after they had fed, I have not found the Filaria 

 at this later period, when in the true Filaria mosquito they abound, and cannot readily be 

 overlooked. I would not be positive on this point, as my observations on the tiger 

 mosquito are not sufficiently numerous ; but my impression is that both species are 

 incapable of acting as efficient intermediary hosts. 



The true, or what I believe to be the true, Filaria mosquito is a brown insect, about -^ 

 of an inch in length, snuff-brown in colour, without any particular markings whatever. 

 In some specimens, and especially some days after feeding, and when her eggs have been 

 deposited, there is an appearance of banding about the abdomen ; but there are no 

 distinct markings, as in the case of the tiger mosquitoes. It appears to thrive best when 

 the thermometer ranges from about 75-84° Fahr. In the very hot weather it dis- 

 appears, or is languid, and the rate of maturation of the ova (in those specimens one can 

 procure) is too quick apparently for the metamorphosis of the Filaria. Consequently, 

 experiments in June, July, and August may not be uniformly successful. In Amoy, 

 September and October are the best months for observations on this species. The 

 female alone is the blood-sucker. She feeds but once if not disturbed, and lavs her egg 

 about the fourth or fifth day afterwards. Some lay on the third clay, and some do not 

 part with their ova till the seventh. As a rule, they die soon after laying, but a few 

 survive till the sixth or seventh day, and in these alone is the metamorphosis of the Filaria 

 completed. Perhaps one mosquito in ten attains this age, at all events in confinement. 

 Possibly in normal surroundings a larger proportion survive. 



On commencing the study of the metamorphosis of the Filaria in the mosquito the 

 first circumstance that strikes one is the largeness of the number of Filaria? ingested by 

 the insect. In a corresponding quantity of blood, drawn in the usual way from the 

 finger, not one fourth part of the number contained in the blood of the insect's abdomen 

 would be found. It is quite a common thing to find 30 or 40 Filarial in the minute 

 speck of blood we express from the abdomen. Often this number is exceeded, and more 

 than once I have found them literally in hundreds. This indicates that the mosquito 

 in some way or another is adapted for fishing the Filaria out of the blood stream. The 

 proboscis of the insect, as it lies in the lumen of the vessel from which blood is being 

 imbibed, must tend to arrest the parasites as they are swept against it by the stream, 

 just as a stake in a stream of water accumulates straws and sticks ; and the lashing 



