Entomology for medical officers / by A. Alcock.

  • Alfred William Alcock
Date:
1920
Catalogue details

Licence: In copyright

Credit: Entomology for medical officers / by A. Alcock. Source: Wellcome Collection.

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    the 8th have each a small plate of chitin anteriorly in the middle line, and some or all of those to the 7th have a pair of petiolated rosettes or whorls, or “cockades” of scales (■^§5 16, the fin or brush of hairs in the mid-ventral line of the 9th segment is very bushy. The tracheal trunks open on the 8th abdominal tergum, in a hollow which is bounded laterally and posteriorly by folds or valves that are homologous with the breathing-tube and valves of other Culicince. The larval life is passed in waters of the nature already described on p. 68, most species having their own prefer¬ ential habitat. The duration of the larval stage varies \ under optimum tropical conditions it is about a week, but in cooler climates it extends to three weeks or more, and in tiG. 26.—IN ew-hatched Larva of Anopheles aconitus. northerly latitudes it may last through the winter. In the new-hatched larva (Fig. 26) the hairs are not branched or feathered, and the abdominal whorls or cockades have the form of simple scales (Stanton). The species of Anopheles have been segregated in numerous very questionable genera, chiefly according to the form and distribution of the scales. Certainly there is an obvious graduation from all-brown, unspotted, hairy species like Anopheles bifurcatus to brightly coloured, profusely spotted, scaly species like Anopheles pulcherrimus; but the steps of the series, though highly interesting to the zoologist, are stumbling-blocks to the systematise and are a snare and a delusion to those who merely wish to identify the species known to be noxious. Unfortunately the mutable and
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