Saturday, October 18, 2008
I decided to photograph and talk about a toad dissection I did this week. Some people (Lorelei?) might not want to see these pictures. A few of the Queenslanders amongst you are likely to have done a toad dissection at school. I wish I could preface this entry with some illuminating comment on the ethics of dissection, but in order to do this sort of thing I try not to think too hard about the morals of what I'm doing. Sometimes I feel a sympathetic pain in the same body part as the part of the animal I'm cutting. I am a hypocrite. But enough of my moral flabbiness, and on with the toad.
Here's my toad. I picked it out of the other toads in the tub because it was a very pretty shade of pale yellow. It's illegal to breed cane toads, so the toads we used were captured in Northern Queensland and crated down.
This is always the saddest part of the dissection.
Once I've made the first cut it's easier to think of the toad as a specimen, and not an animal. Here (above) I've cut through the skin to reveal the abdominal muscles. Toads have no external genitalia (both sexes have a multi-purpose cloaca), so it's only once you get inside that you can tell what sex it is. This is a male toad, because it has a vocal sac. You can see the vocal sac in the photo immediately above. It's the black-and-white flecked section of skin beneath the lower jaw.
These pictures were taken after I cut through the muscle layer. The internal organs are known collectively as the viscera. In the above picture, where the chest muscles and vocal sac have been severed, you can see the white roof of the toad's mouth.
Here's a close-up of the viscera. The following organs are visible:
Lungs: the pale yellow, honey-comb sacs on either side of the body. As well as breathing with their lungs, toads can breathe and absorb water through their skin.
Heart: dark red, in the centre of the chest.
Stomach: pale pink tube on the lower right hand side of the photo. It is attached the small intestine, which is the thinner, coiled tube.
As it turned out, there was something wrong with my toad. The large grey ball in the middle of the viscera is the gall bladder, which is abnormally enlarged. Normally the toad's liver would be dark brown-red and cover a large portion of the viscera. However, this toad's liver is visible as the two shrunken, pale brown masses on either side of the gall bladder. Humans with poor liver function can have a yellow complection. Maybe the yellow colouring I initially took to be the sign of a particularly beautiful toad was actually a result of liver disease. The demonstrator told me that if my toad was a human, it would be an alcoholic.
At this point my camera ran out out of batteries, so I can't show you the toad's kidneys, which were located under the rest of the viscera, or its internal testes, which are small yellow things that sit above the kidneys. Neither can I show you inside its heart, which I had to remove, slice through and put in a petri dish. Underneath the viscera I could see the toad's backbone sitting against its skin. I ran out of time to draw the nervous system, so I wanted to take the toad home in my lunchbox to finish the prac, but the demonstrator wouldn't let me.
Next week I'm doing a pigeon.