Listening audioscript

23. WHAT IS THE LECTURE MAINLY ABOUT? 
24. ACCORDING TO THE LECTURE SEA CAVES ARE MOST OFTEN 
FOUND IN WHAT KIND OF AREA? 
25. ACCORDING TO THE LECTURE LAVA CAVES FORM WHEN: 
26. ACCORDING TO THE LECTURE, WHAT ARE TWO FACTORS 
NECESSARY FOR THE FORMATION OF A SOLUTION CAVE? 
27. ACCORDING TO THE LECTURE, WHAT MAKES IT POSSIBLE
FOR RINGS OF LIMESTONE TO BEGIN FORMING ON THE CEILINGS OF 
SOLUTION CAVES?
28. LISTEN AGAIN TO PART OF THE LECTURE. THEN ANSWER
THE QUESTION. 
(Professor)
These kinds of caves can be seen all over Hawaii, as you might expect. 
The longest lava cave is Kazumura Cave in Hawaii, a cave system that is 
almost 30 miles long.
Why does the professor say this?
 (Professor)
…as you might expect. 

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Page 526 [ mp3 262-263] 
 
Questions 29 through 34. 
Listen to a discussion in a biology class. 
(Professor) 
Okay, so yesterday we discussed the eye structures, light spots, 
structures that can only sense light but can’t see images as humans do. 
For class today, I want to look at compound eyes. And um, today we’ll 
look at one example of a compound eye by looking at the eyes of 
butterflies. Butterflies have compound eyes made up of thousands of 
ommatidia. [ä-mə-ˈti-dē-ə] Each ommatidia collects light and perceives a 
picture. This allows the butterfly to look forward, backward, and to the 
sides all at the same time, but we are finding out they might be doing 
more. 
First, let’s look at the compound eye of a butterfly in this drawing. The 
compound eye is a very interesting structure. Um magnified, the eye 
looks a bit like a…a pincushion full of round-headed pins. The surface of 
the eye is curved and made up of thousands of ommatidia. The 
ommatidia are lenses, and they cover the surface of the compound eye. 
Now, we said that the ommatidia are lenses, but they’re not flat lenses, 
they’re lenses with a number of sides. There are thousands of ommatidia 
on the surface of a compound eye; each ommatidium [ä-mə-ˈti-dē-əm] 
has a curved surface with six-sided lenses, and the six-sided lenses 
allow each ommatidium to face a slightly different direction and sense a 
slightly different image. As light enters each lens, photoreceptors under 
the lenses send messages to the brain. The brain reconstructs the image 
of the butterfly’s surroundings by combining the thousands of messages 
from each of the thousands of lenses into one image. 
Now, let’s talk about what a compound eye actually sees; a compound 
eye can see movement well, but it does not focus well. Butterflies are 
very nearsighted, so their eyesight isn’t very clear, yet they’re remarkably 
able to detect movement. Have any of you tried to catch a butterfly in 
flight? Or possibly some of you have been frustrated while trying to swat 
a fly? Researchers have known for a long time that insects of all kinds 
can sense movement very well. The compound eye allows insects to 
detect the slightest movement much better than our eye can in spite of 
the fact that it doesn’t focus well.
And it’s now believed that a compound eye probably sees one image 
rather than a compound picture. At one time it was thought that a 
compound eye saw a compound picture. Some thought that monarchs 
and other insects could detect movement well because each 
ommatidium registered six complete images, so the monarch saw some 
6,000 pictures of the same item. This would be a bit like standing in a 
store and looking at a wall of TVs all tuned to the same channel. Every 
movement on the screen produces thousands of like movements. 
But now…uh…most researchers think something different is happening; 
they think that a compound eye sees one image that is blurred because 
of the huge number of lenses in the compound eye. Because the eye 
senses light from so many directions, the butterfly detects movement 
easily. The slightest movement alters the light sensed in hundreds or 
thousands of the ommatidia, allowing the butterfly to react quickly, even if 
it can’t clearly see what it’s reacting to. 

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Also, butterflies have the broadest visual spectrum of any known animals 
and they are also able to perceive polarized light. And recent research 
indicates that this ability to detect polarized light aids butterflies in 
migration and finding a mate. Polarized light, for those of you who don’t 
remember, is light that is reflected or transmitted through particular 
mediums and as a result the light waves are condensed to a single range 
of light in the ultraviolet range. Navigation is important for numerous 
species of butterflies, especially for those that migrate. It is known that 
butterflies navigate using the sun as a compass in the same way that 
many birds also do. However on overcast days, not being able to see the 
sun might present some problems in navigation. On a cloudy day, many 
ranges of visible light are blocked by the clouds, but like I said earlier, 
polarized light is light that has passed through a medium, in this case 
clouds, and condensed into the ultraviolet range, which is able to 
penetrate clouds. Because butterflies can see polarized light, they are 
able to navigate even in cloudy conditions, something that birds can’t do.
 
And in terms of finding a mate, there is new research that provides the 
first example of mate recognition based on certain species of butterflies’ 
ability to detect polarized light. These species of butterflies live in very 
dense rain forests, and the lush vegetation makes it difficult for butterflies 
to detect each other because they blend in with the dark green 
background of the rain forest. But luckily for these butterflies, the females 
have layers of transparent scales on wings that transform the visible light 
into a brilliant blue polarized light. And because of their eyes’ ability to 
detect the polarized light, male butterflies are able to pinpoint the location 
despite the dense vegetation of the rain forest.