XII] LIFE-CYCLE 221 



arise two spicules of unequal length. The female is 25-30 cm. 

 in length, by 1-1*3 mm. in breadth. The tail is short and 

 blunt, and the vulva is situated near the origin of the intestine, 

 a distance of about 7 mm. from the mouth. The eggs hatch 

 in the uterus, liberating embryos about 285 to 295 /* in length, 

 by 5 ft in breadth ; their anterior ends are somewhat tapered, 

 whilst posteriorly the body tapers off into a long and delicate 

 tail. 



Life-cycle. As in the case of F. bancrofti, the embryos of 

 F. immitis are liberated into the blood and appear in the 

 peripheral circulation. According to Manson the embryos of 

 this species, as in bancrofti, are more common in the blood 

 during the night, thus exhibiting a nocturnal periodicity, but 

 this is denied by Fulleborn. If the embryos are injected into 

 the blood of a healthy dog, they will persist in the circulation 

 for several months. 



Fig. 58. Part of the Malpighian tubule of an Anopheles claviger, infected 

 with the embryos of Filaria immitis. (After Noe.) 



