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700 immitis, whose larvæ circulate in the blood and are taken up by mosquitoes in the same way as F. bancrofti. (Fig. 109.) Grassi and Noè (confirmed by Bancroft, Sambon, and Low) have shown that the embryo F. immitis passes through the earlier stages of its metamorphosis in the Malpighian tubes of



Anopheles, whence, on attaining a certain stage of development, it passes forwards to the head of the insect, where it behaves in much the same way as F. bancrofti.

Parental forms.—The parent filariæ have been found many times. They are long, hair-like, transparent