276 EVOLUTION AND DISEASE. 



by a series of well-planned experiments, has demon- 

 strated that this insect acts as the intermediate host of 

 the parasite. During the following four or six days the 

 embryos complete their metamorphosis, and the friendly 

 mosquito has completed its life cycle and dies, and its 

 body probably falls into the water in which the eggs were 

 deposited. The filaria by this time has developed so far 

 that it is capable of living independently of the mosquito, 

 and it seems probable that it remains in the water until 

 it is captured by some animal in search of food, or 

 swallowed by man, thus enabling it to complete its 

 development. 



These facts indicate conclusively that this disease 

 is spread and, in all probability, maintained by mos- 

 quitoes, and the geographical distribution of the disease 

 is coincident with that of culex. In this connection it is 

 a fact of some importance to remember that filariae occur 

 in other animals as well as in man. Manson states that 

 half the dogs in China, all the magpies, one-third of the 

 crows, and many other birds harbour similar hsematozoa 

 in prodigious numbers ; and in South China where the 

 filarial disease is endemic, if the blood of one thousand 

 natives, selected indiscriminately, be examined some 

 time between sunset and sunrise, in about one hundred 

 the Filaria sanguinis hominis will be discovered. 



The point of interest to us in connection with this 

 disease is that though the filarise occur in dogs, magpies, 

 and I have detected them in the blood of macaque 

 monkeys, the enormous enlargement of the legs and 

 other parts of the body, which is one of the chief cha- 

 racters of the disease in man, has not been recorded in 



