Spiders No.17 - The Inner Eye Revealed !

[Walter Piorkowski]

Leitz Ortholux microscope
4X Leitz projection eyepiece plus 1/3x relay lens

Image No. 1
231 images at 2.5 micron increments
Nikon 10x Achromat objective
Diffused Fiber Optic illumination

Image No. 2
55 images at .001 inch increments
Leitz UO 6.5 X achromat ULTROPAK objective
Diffused Fiber Optic illumination

Image No. 3
169 images at 2.0 micron increments
Leitz 23X Apochromat ULTROPAC objective
Diffused Fiber Optic illumination

Image No. 4
Crop of image number 1

Canon 50D
Zerene and Photoshop processing.



Getting a detailed image of a spider’s eyes has long eluded me. However, all of the technical challenges have now been solved and I present my best images of this subject to date.

Studying these images I believe that this spider sees the world through the equivalent of eight fish eye lenses. I have come to this conclusion based on the amount of refractive distortion, similar to looking into the front of a fish eye lens, seen in on and off axis eye images. These differences are seen in image number one and comparisons with image three and four.

The subject for these images was chosen first for the clarity of the eye lens, which I was determined to show. It also has minimal hair in the ocular area. The spiders seem to show as much diversity in their eyes as they do in body types. This will be illustrated in future posts.



Top image, No.1:
All eight eyes are present in this image. At first look the top four, two lower center and two lower outer all seem to be different. The top four eyes as viewed from the side reveal the shape of the clear lens and the unexpected concave terminated cylindrical retina underneath.

The eye covering, if it is a lens, should affect how we see the subject inside. The lower four eyes are seen from an almost top view. From this view it appears that the two lower outer eyes may be hemispheric retinas while all the others are concave.

Middle image, No. 2:
More of the host subject to show the eye location on the head region of the carapace. Well developed, hairy chelicera fill the remainder of the image.


Middle image, No. 3:
I hesitated to put this image in because the high magnification has pushed both the optical and stacking systems to their limits. This image is of the four eyes on the right side of image number one with the subject rotated 90 degrees. There is a slight change in angle also from vertical. The change in angle helped to clear up whether the pair of hemispherical shaped retinas in the top image where truly that shape. In the end they all turn out to be some form of concave cuplike retinas.

Lower image, No. 4
A crop of the right side of image number one, rotated 90 degrees to match image number three. Note the difference in how the upper right, retina appears in the two images.

I am excited to show these revealing images. Enjoy

Walt

[john sp.]

Wow, that is very cool what you've been able to illustrate with your photos. I appreciate you walking me through what I'm looking at; so, I can better understand the significance. I say this naively, because I have no special knowledge of spiders, but I found myself wondering if they were capable of shifting the direction in which the eye is looking to some degree, either by moving the internal retina or by moving the whole eye. I suspect not, because they seem to be arranged in an array to provide a wide field of view.

It is interesting how the four smaller eyes in the center appear to provide a wide view, the two larger eyes near the front seem to look straight ahead, and the two large eyes to the side seem to be for peripheral vision. (I may be misjudging the relative size of the eyes to each other, but they appear to be four smaller and four larger eyes in the second picture, in particular.)

John

[Walter Piorkowski]

Hello John. Glad you enjoyed the images. I have read that spider scientists divide up the eight eyed spiders ocelli into main and secondary ocelli. While hunting, the secondary are used to catch the motion of prey, having a broader field of view. The main, larger ocelli are focused on the prey while moving in for the kill. If they move I don't know.

Jumping and crab spiders have eye size differences large enough to easily see. Most others like this are less obvious. Makes this kind of photography more interesting.

Walt

[rjlittlefield]

Walter, these are superb images! I wonder, do you have a copy of "Biology of Spiders", by Rainer F. Foelix? It is crammed full of scientific information. I think you would find it fascinating reading.

I found myself wondering if they were capable of shifting the direction in which the eye is looking to some degree, either by moving the internal retina or by moving the whole eye.

They do, by moving the retina, at least in the more advanced groups. See summary HERE.

--Rik

[Cactusdave]

Very clever images. Nice to see the Leitz Ultropak being put to good use. I have found it to be an exceptionally effective epi illumination system despite its age.

[Mitch640]

These are all fantastic images. Has anyone ever done anything like this before? It seems cutting edge to me. And I am glad the question was answered about whether they can change the direction they look. I have watched fly eyes and dragonfly eyes, and have witnessed that something is moving behind the multi-facets on the outside. I would really love to see whats inside there.

[lauriek]

Wow!

[rjlittlefield]

I have watched fly eyes and dragonfly eyes, and have witnessed that something is moving behind the multi-facets on the outside.

That one is actually an illusion. It happens because what you see in each facet depends on the angle. If either you or the bug moves, then what you see through the facets changes, and that gives the illusion of something moving inside the eye. In some insects, there is a tiny movement within each ommatidium to adjust light sensitivity, but that's a fairly slow process -- many minutes. The effect can be dramatic, however. See HERE and follow the links to earlier postings.

--Rik

[Walter Piorkowski]

Gentlemen. Thank you for your interest in my post and Mitch, you are too kind. Rik, your referances, as usual, are excellent. I only have one old childhood book on this subject and I will look into your suggestion.

Dave, I think the Ultropak system is one of the best. Still working on aquiring additional objectives and parts.

Laurie, I have long admired your work and congradulations on your recent Bioscapes awards.
Walt

[rjlittlefield]

I only have one old childhood book on this subject

Ah, then you are missing a treat in Foelix's work. You can see some of it using Amazon's "Look Inside" capability. Simply search on "sense of vision plays only a minor role in behavior", including the quotes. This will take you to the start of the vision section, which begins on page 82.

By the way, I learned today that there is an updated version of the book that is being released on Dec 31. I did a search for that same phrase in the revised edition and discovered that it appears on page 102. Checking the overall lengths, I see that about 100 pages have been added to the new edition. It would be worth waiting for!

--Rik

[Walter Piorkowski]

Yes Rik, I saw the same new 2011 version notice. Looks like we will both be reading a new third addition sometime next year.
Walt