It is generally admitted that the ability to determine the species of Anopheles by an examination of their larvae would place a valuable weapon in the hands of the practical sanitarian in tropical countries. In the investigation of an area for the determination of the Anopheles present, it frequently happens that, on account of their habit of concealment by day, adult mosquitos are difficult to find, whereas their breeding places may be located readily. If the larvae are transported to a distance they commonly do not develop further, and so, failing the specific identification of the larvae themselves, valuable information is lost. It is therefore very desirable to know whether, and to what extent, any of the characteristics of such larvae may safely be employed in determining their species.