Sunday the 6th of December, Natalie and I had to dissect worms for a science experiment. We started setting up at about 3:00 o’clock, when Dad was hanging upside down
doing back exercises and Mom and Beth were getting ready to take the dog for a walk. Natalie and I had to find the dissection kit before we could start, so we went downstairs to the room where we keep the science supplies. I got down all the boxes that had supplies in them and looked in them before handing them down to Natalie, to see if there was anything we needed inside. Finally when the last box we looked in had what we needed, I put all the boxes, in which we had found two spiders, back on the shelf.
We set down some news paper on the table in case we splattered any “worm juice”. Then, we put the dissection boards down and got our worms. Since we bought them in dirt we rinsed them off in some water before setting them on the boards. This action did not do much to slow them down. They kept crawling to the edge and under the boards; which wasn’t much of a problem until we started dissection. Before starting the actual dissection, we felt their setae on the outside bottom edge of the worm. The setae are hooks that anchor down one end of the worm while the other moves back or forward. This is how the worm moves.
The next step was to pin the worm down by both ends. Natalie managed to do this while the worm was wiggling, but I was less successful. In the end it was fine that I couldn’t get it to hold still while alive, because Natalie’s worm was wiggling despite its restraints, and because of that, beginning to tear a hole in itself. Dad said that we would put them in rubbing alcohol to suffocate them, so they would be easier to dissect.
After that, it was much easier to pin the ends down, we did this with the top side of the worms up. Next, we used small scissors to cut the skin from about an inch behind the clitellum all the way to the anterior end. The clitellum is a barrel-shaped swelling that usually starts at the thirty-second segment and covers all segments up to thirty-seven. This structure aids in reproduction, and helps distinguish the head form the tail. We were able to do as the book said and not cut any organs in the process.
The inside of the worm looked a lot like the inside of a fish to me. After making the cut, we cut the septa that connected the intestine to the inside of the skin and once they were free, pinned the skin down away from the intestine.
The first organ we were supposed to identify was the pharynx. That is what the worm uses to suck in the dirt that it gets its food from. Next we were to find the esophagus. The esophagus was covered in small yellow sacks which turned out to be the seminal vesicles. We also had to find the crop, the gizzard, and the intestine.
The crop was behind the esophagus and behind the crop, looking like a larger version of the crop, was the gizzard. The intestine was the yellowish brown tube like thing that ran along the rest of the worm. After finding the main organs we had to find some smaller organs that were underneath some we had already looked at. To see these, we had to cut out the larger ones that were on top of them. The first things I took off were the small yellow sacks that were on top of the esophagus. I think these were the seminal receptacles. I used tweezers to remove these, then the esophagus. Underneath and in between where the seminal receptacles and esophagus were was where the seminal vesicles were. These were a little more difficult to see. Next, I cut about two more inches of skin towards the posterior end. I did my best to remove the intestine without tearing the septa. I was supposed to find the nephridia –which function as kidneys and are located in every segment of the worm– and I thought I had for a moment, but I am pretty sure now that it was actually the ventral nerve cord.
I took out all my pins and threw the worm away. While Natalie finished her dissection, I washed my tools and when she was done I washed the ones she brought. Natalie said she would put everything away. We spent about an hour and a half over all, including the washing up. When we were done, dinner was ready and the rest of the evening was very relaxing. It was a first time experience for me, to have names of organs and substances going through my head and my knowing what so much of it was used for inside the animal. Natalie and I are next going to be studying, and probably dissecting a crayfish, but we might get a lobster instead!