Which one of the following is characteristic of microfilaria of W. bancrofti?

The features of microfilaria of W. bancrofti are: General appearance: Graceful, sweeping curves. Free cephalic space: As long as broad.   Excretory pore: Not prominent:   Caudal end: Uniformly tapering to a delicate point and no terminal nuclei present.   5. Nuclear column: Nuclei discrete; Important points   Microfilaria of W. bancrofti and B. malayi in India display a nocturnal periodicity. Maximum density of Mf in blood is reported between 10 pm and 2 am.   Man is the definitive host and mosquito the intermediate host of Bancroftian and Brugian filariasis.   Third stage larva in mosquito is infective form.   Adult worm may survive for 15 years or more.   Duration of mosquito cycle (extrinsic incubation period) is between 10 and 14 days.   Main vectors in India are: C. quinquefasciatus (C. fatigans) for Bancroftian filariasis and Mansonia mosquitoes for Brugian filariasis.   Prepatent period: It is the time interval between inoculation of infective larvae and the first appearance of detectable Mf.   Clinical incubation period: Time interval from invasion of infective larvae to the development of clinical manifestations.