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Homology Weekly: Compound Eyes

Wednesday, October 28th, 2009 | Ants, Comparative Anatomy, Homology Weekly, Morphology | 9 Comments

iGigantiops destructor/i (Michael Branstetter - www.antweb.org)

Gigantiops destructor (via Michael Branstetter - www.antweb.org)

The lateral eyes of adult insects (and most Arthropods) known as compound eyes, are like no other visual organs found in animals. You can think of our vertebrate eye as a simplified, one-lens photographic camera with a sensor composed of millions of light sensitive cells (and a blind spot, mind you). Well, that’s nothing. Each insects eye is composed of several small photographic cameras, each with its own lens and light sensitive cells (albeit, commonly only six of these). These units are called ommatidia (sing. ommatidium), and the image if formed by the combined information from all of them.1

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  1. To be honest, I have never know if this visual organ is called compound eye because it is composed of several ommatidia or because each ommatidium is composed of several elements. This has never disturb my sleep though.
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Homology Weekly: Tentorial Pits

The anterior tentorial pits (arrows) in a <i>Tetraponera aethiops</i> worker (Scanning Electron Micrograph, Roberto Keller/AMNH)

The anterior tentorial pits (arrows) in a Tetraponera aethiops worker (Scanning Electron Micrograph, Roberto Keller/AMNH)

The head of an ant in frontal view has a couple of holes usually located in the area between the mouth and the place where the antennae are inserted. These holes look intriguing from the outside– Are they part of a sensing organ? Do they secrete a special chemical signal or defense substance through them? Are they use for breeding? The answer is more mundane than that. As I mentioned in an earlier post, most of what one sees in the outer surface of the arthropod’s exoskeleton does not have an external function, but is rather a symptom of the inside working in these wonderful machines. These particular holes mark the places where the cuticle invaginates to form the internal skeleton of the insect cranium known as the tentorium. The external holes produced by these invaginations are thus termed the tentorial pits.

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And as we discussed last semester, the Army Ants will leave nothing but your bones.
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