Posted by: Rob Viens | August 30, 2012

The Immeasurable Beauty of a Shark’s Eye

This week Darwin’s diary entries are rather short and mostly about surveying and the weather, yet his Zoological Notebook has been overflowing with descriptions of a range of different forms of sea life.  For example, his diary entry today is rather basic:

“Very wet day: about noon it fell calm, & we could hear the surf roaring although about six miles distant from the beach.— The weather looked exceedingly threatening; but after all it did not blow more than a stiff breeze during the night.” (Aug 30)

But I am still catching up on his many zoological entries. Here is a short one from a couple of days ago:

“August 28th. Lat 38°.25′ S. Soundings 14 fathoms. Caught by a hook a specimen of genus Squalus: Body “blueish grey”; above, with rather blacker tinge; beneath much white:— Its eye was the most beautiful thing I ever saw.— pupil pale “Verdegris green”, but with lustre of a jewel, appearing like a Sapphire or Beryl.— Iris pearly edge dark.— Sclerotica pearly:— In stomach was remains of large fish.— In the uterus the young ones for a long time after the viscera were opened continued to move: good specimen for dissecting” (Zoological Notebook)

Head (and eye) of a spiny dogfish (from NOAA):

Spiny dogfish

The “Squalus” that Darwin describes here almost certainly refers to the group of sharks known as dogfish (Family Squalidae).  There are several types of dogfish – not all of which are in the same family.  Some that live in the area south of the Río de la Plata, include the spiny dogfish (Squalus acanthias), Cuban dogfish (Squalus cubensis), and the smooth dogfish (Mustelus canis).  I’m not sure if one of these species has eyes that stand out in the way that Darwin describes, but from general descriptions it could have been any of them.

Cuban dogfish (from Florida Museum of Natural History – photo by George Burgess)

Cuban dogfish

I have three comments:

  1. I absolutely love his fascination with the shark’s eyes, and the attention to describing the details of the color.  To find such poetry in the eye of a shark speaks volumes about Darwin’s love of nature.  It is a beautiful thing.
  2. I distinctly remember dissecting a dogfish in college biology many years ago, and much like Darwin, I was fascinated by the fact that it was filled with little baby sharks.  I must say, it disturbs me a little now, but at the time I was so fascinated I remember bringing one of the little ones home.  I have no idea what ended up happening to it.
  3. I’m not so sure what to make of “good specimen for dissecting” but I am intrigued by this statement.  What was it that struck Darwin about the dogfish that made it so good for dissecting?  Was it the ease?  Or the interesting things that he found inside?  There must be something particularly “good” about dogfish for dissecting because I know (that much like in my case) it is a common species for intro biology students to dissect. You heard it first from Darwin himself…

Anyway, may all your dissections be good ones and all your dogfish have beautiful eyes! (RJV)

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Responses

  1. I, too, have been up close and personal with dogfish sharks in the laboratory but I have never waxed so eloquently about their eyes. Perhaps I missed something?

    I liked the dissections because, in some respects, there was a relatively simplicity to their insides and the structures were generally large and easy to find, e.g., the enormous liver, spleen, the rectal gland and the claspers in the male. In addition, their musculature is so elegantly arranged that it speaks volumes about their streamlined bodies.


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