Hatching Of Larvae

A cap like piece of the thick end of the egg shell is split off. This cap is not defined on the egg, but the separated portions are of about the same size.

The larva consists of head, thorax, and abdomen, and on each of these parts structures occur which are in themselves of great interest and are of great importance in the identifying of larvae. The head is globular; in the newly hatched larva it is very dark, and it is only later that it becomes lighter and that the chitinous patterns, often characteristic in arrangement, appear; and its size proportionately to the thorax diminishes, so that eventually the thorax is larger than the head. Further, in the young larvae the important structures known as palmate hairs are imperfectly developed, but larvae newly hatched can at once be told from those of Culicidce by their characteristic horizontal position. The head is inclosed in a chitinous covering which, posteriorly, where the neck is inserted, is defined as a broad blackish collar. There is a slight fissure in this band dorsally, and it is from here that a V-shaped line diverges. This V often has grouped about it patches of pigment arranged in so characteristic a way that one is enabled to identify the species sometimes by this means alone. Thus A. maculipennis has a T-shaped pattern, while A. punctipennis has three transverse bands. Arising from two lateral protrusions on the anterior portion of the head are the antennae. They consist of a single rod shaped, somewhat curved body, bearing at the extremity two leaflets or bristles between which arises a branched hair. The antennae is covered with small spines, particularly along the inner border, where they are arranged in pairs. At the junction of the proximal and middle third is a papilla bearing a hair. This hair is of importance in the identification of larvae. Here again very few of the Anophelince have been so far examined, and the only data are those of Christophers and myself regarding the Indian Anophelince. We find that-(1) In the majority of the Anophelince it is simple and unbranched or even absent, while (2) in A. lindesayi it is short and tufted, and in Mr. barbirostris it is long and distally branched. These differences enable one to separate out these larvae by inspection with a low power of the microscope, which is often a matter of great convenience. Of more importance than these hairs are certain hairs which occupy the most anterior portion of the head and may be called frontal or clypeal hairs. These hairs must not be confused with others which lie behind them. Thus slightly behind the level of the antennae may be found a row of six branched hairs, and behind these again a row of smaller branched hairs, which are, to a certain extent, variable in different species. It is, however, the variation in the clypeal hairs that affords a ready and important means of distinguishing species. Anophelince, which in the adult stage may closely resemble one another, may be quite different in their larval characteristics, and if we are right in assuming that difference in oval and larval structure constitutes a specific difference even if the adults closely resemble one another, then in these hairs we often have a ready means of distinction. Where there is no question as to the identity of the imagos, we have in these larval characters a mode of easy identification, though it does not follow that different species can all be distinguished by these larval characters. These hairs project from the anterior margin of the head and directly overlie structures which we shall mention later, known as the "shaving brushes." The clypeal hairs are generally four in number, two arising from the extreme point near the middle line and two from the lateral angles of the clypeus. There may also occur two small hairs, making a total of six, immediately behind the anterior set. The following variations may be found: 1. The clypeal hairs may be quite simple-i. e., unbranched; e. g., M. rossii, N. stephensi, M. culicifacies, M. listoni, M. turkhudi, A. bifurcatus. [In A. bifurcatus variations in these hairs have been described by Ed. Sergent. Thus among 46 larvae examined, three types were found: (1) Eighteen with both hairs simple; (2) 25 with the inner hair simple and the outer hair with two or three terminal branches; (3) three with both hairs slightly branched along their whole extent.] 2. The clypeal hairs may show slight branching, varying in degree in different species; thus in N. maculipalpis and P. superpictus it is but little developed, while in P. jeyporensis it is more regular and better developed. 3. The outer pair may be markedly branched, the median pair having a few inconspicuous branches; e. g., Ce. pulcherrima and Myz. pseudopictus. 4. The other pair may be developed into a close tuft or cockade; e. g., Myz. sinensis, Myz. barbi rostris, A. punctipennis, A. maculipennis. (In the last the central hairs are figured by Grassi as not actually branched, but as splitting up at their ends into several filaments, while Nuttall and Shipley figure them as distinctly branched. The larva of M. turkhudi, aberrant in so many other ways, is peculiar in that the small hairs behind the clypeal set, instead of being short and inconspicuous, are long and easily seen. It may be well to state here that the hairs should be examined when the shaving brushes are in a retracted position.)

We may briefly consider the mouth parts of the larvae, though they do not suffice for distinguishing species. Situated laterally just beneath the lateral pair of clypeal hairs are two conspicuous whorls or tufts of dense hair, resembling a shaving brush in appearance. These are the feeding brushes; they can be turned downward and inward to the center, and assist in producing the flow of food particles into the mouth. While feeding, they are flexed and extended with great rapidity, and on the cessation of feeding they are rapidly extended, as if with a quick jerk. Below the feeding brushes we find on either side the mandibles, then the maxillary palpi, and most ventrally the maxillae. These come inward and almost meet in the middle line, forming the floor of the mouth. Between them and slightly posterior in position lies "the under lip" of Meinert, conic in shape, and bearing teeth, which, as we have seen, are of generic importance in some of the Culicidce, but with regard to the Anophelince no data exist. The mandibles bear stiff hairs directed inward to the mouth, and they serve to "comb " the feeding brushes. Further, on the maxillae there are a set of fine teeth which are probably used for the same purpose. It should be added that the larva generally rotates its head through an angle of 180° when feeding, as may be observed by watching the process under a low power of the microscope, placing the larva for that purpose under a cover glass or in a watch glass.