Les phénomènes de pseudopupille dans l'œil composé deDrosophila (original) (raw)

Summary

In the compound eyes of the fruitfly_Drosophila_, the dioptric system of each ommatidium is able to form virtual images of the receptor terminals (rhabdomere tips) throughout the whole depth of the eye. It is shown (§ 3) that 3 characteristic superposition phenomena occur for images formed by distinct ommatidia (Figs. 3b and 5). The most remarkable superposition appears at the point where the optical axes of all ommatidia converge (center of curvature of the eye). At this level, highly magnified virtual and erect images of corresponding rhabdomeres are superimposed, giving rise to a_deep pseudopupil_ (Fig. 9). Since in the ommatidia of_Drosophila_ the rhabdome shows a pattern of 7 distal endings (Fig. 8a), the resulting_deep pseudopupil_ consists of 7 light spots with a similar pattern (Figs. 8b, 7, 11). Conversely the_deep pseudopupil_ of compound eyes which have fused rhabdomes consists of a single light spot (Fig. 19). Such pseudopupils can be best observed either with antidromic or with orthodromic illumination of the eye, according to the specific transmission or reflection properties of the rhabdomes.

The_deep pseudopupil_ of Dipterans is not to be confused with the_corneal pseudopupil_ (Fig. 13 a) and especially not with the_reduced corneal pseudopupil_ observed with a reduced aperture of the microscope (Fig. 13 b), in spite of the remarkable similarity of these phenomena regarding the asymmetry and the dimension of their pattern (comp. Figs. 7 and 13b). The_reduced corneal pseudopupil_ consists of 7 facets whereas the_deep pseudopupil_ consists of 7 virtual images of the receptor endings.

From the results of Kirschfeld (1967), the appearance of a_reduced corneal pseudopupil_ like Fig. 13 b on the eye of_Drosophila_ proves that 7 receptors located in 7 neighbouring ommatidia look in the same direction in space (Fig. 14). The existence of such an optical arrangement favors the view that the eye of_Drosophila_, like that of_Musca_, belongs to the “neural superposition type”.

A comparative study between the_deep pseudopupil_ and the_reduced corneal pseudopupil_ leads to the following geometric relation, which is specific of the_Drosophila_ eye and probably of all compound eyes of the “neural superposition type”: \frac{D}{e} = \frac{R}{{f'}},$$

, where_D_ is the diameter of a facet,e the distance between the centers of two neighbouring rhabdomere endings,R the radius of curvature of the eye, and_f′_ the focal length (in air) of a corneal lens.

Other types of pseudopupils, commonly appearing as dark spots in compound eyes, are explained on a basis similar to the_deep pseudopupil of Drosophila_ (§5). In fact, the dioptric system of an ommatidium can give virtual images not only of its distal receptor endings but of the whole intensity distribution (i.e. the whole “luminous structure”) which is present in its internal focal plane. If this structure is simple, the_deep pseudopupil_, resulting from superpositions of virtual images, is likewise simple (Figs. 16 and 17). If the “luminous structure” is complex, as for example in the eye of the butterfly_Vanessa_ (Fig. 18a schematized in Fig. 18c), then the_deep pseudopupil_ shows the same complexity (Fig. 18 b and d).

In compound eyes which lack screening pigment between their crystalline cones, one can see_secondary pupils of the 1st and 2nd order_ as described by Exner. Again they may be explained by superpositions of virtual images in the depth of the eye, according to Fig. 20. Moreover, the_deep pseudopupil_ of the “optical superposition eye” may be due to the fact that the more distal converging system of an ommatidium forms virtual images not of the rhabdome endings themselves but of real images of these endings (Fig. 21).

Although the phenomenon of the_deep pseudopupil_ is not perceived by the animal, it is of interest for the experimenter who can use it: 1) to study the light receptors easily in the eye of live and intact animals, 2) to measure the physiological divergence angle between adjoining ommatidia, 3) to study the movement of the visual axis and the retinomotor adaptation of the receptors, and 4) to stimulate simultaneously many_corresponding_ receptors belonging to different ommatidia. The advantages of this_in vivo_ technique are discussed in § 6.3.

Access this article

Log in via an institution

Subscribe and save

Buy Now

Price excludes VAT (USA)
Tax calculation will be finalised during checkout.

Instant access to the full article PDF.

Similar content being viewed by others

Références

Download references

Author information

Authors and Affiliations

  1. Max-Planck-Institut für biologische Kybernetik, Tübingen
    N. Franceschini & K. Kirschfeld

Authors

  1. N. Franceschini
    You can also search for this author inPubMed Google Scholar
  2. K. Kirschfeld
    You can also search for this author inPubMed Google Scholar

Additional information

Partie d'une thèse de doctorat d'Etat es Sciences physiques de l'Université de Grenoble (1971), enregistrée au C.N.R.S. (Paris) sous le N∘ A. 0. 3802.

Rights and permissions

About this article

Cite this article

Franceschini, N., Kirschfeld, K. Les phénomènes de pseudopupille dans l'œil composé de_Drosophila_ .Kybernetik 9, 159–182 (1971). https://doi.org/10.1007/BF02215177

Download citation