Tuesday, September 7, 2010

antenna

The antenna

The antenna are a pair of jointed appendages articulated with the head in front of the eyes or between them. The antenna vary greatly in form; in some insects they are thread-like, consisting of a series of similar segments; in others certain segments are greatly modified. The thread-like form is the more generalized.

In descriptive works names have been given to particular parts of the antennae, as follows (Fig. 5 i):
The Scape.—The first or proximal segment pf an antenna is called the scape (a). The proximal end of this segment is often subglobose, appearing like a distinct segment; in such cases it is called the bulb (a1).

Pedicel—The pedicel is the second segment of an antenna (b). In it differs greatly in form from the other segments.

The Clavola.—The term clavola is applied to that part of the antenna distad of the pedicel (c) ; in other words, to all of the antenna except the 1st and second segments. In some insects certain parts of the clavola are specialised antenna and have received particular names. These are the ring-joints, the funicle, and the club.

Ring-joints.—In certain insects (e.g., Chalcididae) the proximal segment or segments of the clavola are much shorter than the proceeding segments; in such cases they have received the name of ring-joins (c1).

The Club.—In many insects the distal segments of the antennae are more or less enlarged.

in such cases they are termed the club (c2).

The Funicle.—The funicle (e’) is that part of the clavola between the dub and the ring joints; or, when the latter are not specialized, between the club and the pedicel.

The various forms of antennae are designated by special terms. The more common of these forms are represented in Fig. 52. They are as follows: -

1. Setaceous : or bristle-like, in which the segments are successively smaller and smaller,

the whole organ tapering to a -point.

2. Filiform : or thread-like, in which the segments are of nearly uniform thickness.

3.Moniliform: or necklace-form, in which ‘the segments are more or less globosa, suggesting a string of beads.

4. Serrate: or saw-like, in which the segments are triangular and project like the teeth of a saw.

5. Pectinate : or comb-like, in which the segments have long processes on one side, like the teeth of a comb).

6. Clavate :club-shaped, in which the segments become gradually broader, so that the whole organ assumes the form of a club.

7. Copitate : or with a head, in which the terminal segment or segments form a large knob.

8. Lamellate: in which the segments that compose the knob are extended on one side into broad plates.

9. Geniculate: When an antenna is bent abruptly at an angle like a bent knee (Fig. 5) it is

said to be geniculate.

10. Aristate: (in house fly) pouch-like with lateral bristle on last clubbed segment.

11. Plumose: (brush-like) in mosquito.

No comments:

Post a Comment