We're going to do a little bit of a deep dive into this, and we're going to start with these big eyes." "This makes up the face of this larval leech." "As I'm looking at it, you can see the eyes are all open and fully functional." "Now, it's a funny thing about leeches." "If you have a dead leech, and you apply pressure with your finger, it'll just release its stomach contents." "I've never killed a leech, but if I was to do it, I'd probably do this." "That's quite enough." "But the eyes are obviously still active, and what it means is that the leech's got a vision system that's actually quite sophisticated." "If you look at the patterns that the little pigments in the eyes are making, you can tell that they've got some very sophisticated algorithms." "And what you'll see in the retina here is actually more than just a simple dark/light thing." "It's actually a very complicated camera that's picking up information about the world around it and, based on that information, it's identifying the leech's next meal." "The larval leech, like all leeches, is blind." "It lives off of blood." "It has to find it." "It has to find it in the dark." "It can only see by emitting a pattern of light." "And in the darkness, the larval leech uses a very sensitive system." "It has a pair of eyes that are sophisticated enough to pick up that pattern and identify it." "This one, on the other hand, is blind, and yet it uses its eyes and it employs a very different strategy." "It's got a pair of eyes that are much simpler." "They're only designed to pick up something that's moving." "And it's very much based on detection." "So it's movement, it's detection." "You might be wondering why." "Why would this baby leech be developing this sophisticated visual system?" "Well, we believe we have some clues from the larval leech of another kind of leech." "We have some clues from the early development of a leech." "And in leeches, there's a very special type of blood cell, this one." "This one." "We call it hemocyte." "And what hemocytes do is they have a special kind of blood cell that's responsible for protecting the blood." 3125841983

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