I thought this first one was pretty interesting, when I made a 3D stereogram from it the internal structure became evident. As I've seen before, the central area is a double-convex lens, but what I hadn't seen before is that the crescent shape on the right is actually a complete ring on its own layer beneath the outer membrane. The axis of the eye runs from near-left to far-right -- through the sphere and then the center of that ring-shaped shelf.
How does a tarantula pull its eye out from all that?
Rik supplied the following diagram from "Biology of Spiders" by Rainer F. Foelix.
Upper side
I'm not sure what I did wrong here but the 3D looks a bit skewed. Still, it can be seen that there are several distinct layers of membrane.
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Heteroscodra maculata adult female, 5-inch, exuvia
Eye of H. maculata exuvia
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Re: Eye of H. maculata exuvia
I agree, this pair does look odd when viewed as 2 separate images. But when viewed in stereo it looks great!papilio wrote:I'm not sure what I did wrong here but the 3D looks a bit skewed.
I think the unexpected "skewed" appearance just comes from looking at a sharply domed structure from two different angles, one of which is far off the axis of the dome.
Perhaps it doesn't. Remembering Foelix's comment that "Beneath a single cuticular lens", I'm thinking that perhaps the spider just forms a whole new lens and throws the old one away. The lens needs to change both diameter and curvature as the critter grows, and it seems like that would be challenging to accomplish otherwise.How does a tarantula pull its eye out from all that?
--Rik
Re: Eye of H. maculata exuvia
Thanks Rik!rjlittlefield wrote:I agree, this pair does look odd when viewed as 2 separate images. But when viewed in stereo it looks great!
I thought that maybe I had picked inappropriate angles, but this makes sense.I think the unexpected "skewed" appearance just comes from looking at a sharply domed structure from two different angles, one of which is far off the axis of the dome.
Excellent point. Generally the spider doesn't leave much behind in the way of structural organs -- it appears that the eyes lead the list, seconded probably by the sex organs. In fact in females the sperm is stored in the spermathecae and the eggs are fertilized only as they pass these organs as they're being laid. Sometimes after we've paired tarantulas the female, though she's gravid, molts before laying and we're out of luck.Perhaps it doesn't. Remembering Foelix's comment that "Beneath a single cuticular lens", I'm thinking that perhaps the spider just forms a whole new lens and throws the old one away. The lens needs to change both diameter and curvature as the critter grows, and it seems like that would be challenging to accomplish otherwise.
[Edit] Come to think of it, something I've noticed when shooting macros of spiders which happened to be about to molt is that their eyes have already begun pulling away from the exo -- that's probably the first sign. Makes sense!