Helping My Sister's Classmates

My sister Kate, about two years my junior, was always interested in plants and flowers, but also bugs and other little critters. It was therefore no surprise that our parents got her a microscope for her last birthday. It was a well-received present, and she studied plant leaves, bread mold, and drops of water from the creek behind the house. You name it, she had put it under her microscope. It was no wonder that biology was one of her favorite subjects in school.

I had just gotten back from college for summer break, and Kate's vacation had not yet started, but her college is nearby, so she still lives with our parents. Our parents were away on holiday by themselves for a week, and Kate and I had the house to ourselves. This was fine with us; the pantry was well stocked, and they had also given us some money for food. We were not going to starve. I spent my free time reading, sunbathing in the garden, and cooking for the both of us.

"What are we having for dinner tonight?" Kate asked during breakfast.

"Not sure yet, why?"

"Well, Julie and Tanya are coming over to study; do you want to cook for them too, or should we order something?"

"Sure, I'll toss something together; summer salad sounds good?" I asked.

"Oh, nice! I'm sure they'll love it!" Kate said as she swung her backpack on her back and left for college.

I had met Julie and Tanya before. Tanya was a pretty, petite redhead with a naughty streak. Last summer, during a camping trip with Kate and me, she convinced us to go skinny-dipping with her, and she also managed to get herself a tattoo even though she was still underage at the time. Julie was more modest and less outgoing, but definitely not less attractive. She was taller than Tanya and had large breasts. Although Julie did not dress provocatively, she usually wore tight shirts or dresses that accentuated her chest.

The rest of my day was rather uneventful. I prepared dinner, put it in the fridge, and went out in the garden to catch some rays. I tried to read, but after half a page, unable to remember the last page that I had read, I put down the book and closed my eyes. It took only a minute or so to doze off.

About an hour later, I woke up to a noise from the house. Kate and her friends had come home. "Hi there, sun worshiper!" Kate exclaimed. As the three of them came into the garden. I stood up and greeted them. They went back inside and went to Kate's room to study until dinner time.

After dinner, we chatted over coffee. After a short silence, Tanya announced: "Julie has a question for you!". I looked over to Julie and saw that her face was turning a bit red.

"Well, we were studying all kinds of stuff under the microscope, and we wanted to...", she stammered. "Eh, study something new, you know..."

"Come on, just say it!" Tanya interjected.

"Well, we wanted to study sperm cells." Julie finished, her face now red as a beet.

"Sperm cells? And how do you want to get those?" I replied, although I was sure I knew the answer.

"From you, silly! You're the only one here that can provide them!" Tanya said she was clearly not patient enough to let Julie answer.

"No way! I mean, do you expect me to ejaculate into a test tube for you? No!" I objected, although I must admit, the thought did excite me.

"Come on, it's for educational purposes!" Tanya said jokingly.

"I mean, I can't just jerk off..." I tried to protest, but Kate interrupted.

"Sure you can; I know you can!" Until then, my sister had stayed out of the conversation. Did my sister just say out loud that she knows that I masturbate?

"Besides, don't you want to know how your swimmers are doing?" Julie added, much less bashful than earlier.

The hypothetical situation was having an effect on me; I was glad that we were still sitting at the table, hiding the bulge in my shorts.

"If I do this, and I mean if," I asked, "will you keep it secret?"

"Yes," "of course," "cross my heart and hope to die!" they answered, speaking through each other.

"One other thing, the three of you are doing the dishes tonight!" It wasn't much, but I figured I had to have some compensation to help hide the fact that I was actually turned on by this. They all agreed.

"I'll go to my room and do it there. What do you want me to use to collect the sample?"

"I'll bring you a receptacle," said my sister.

I went to my room, and Kate went to her own room. A few minutes later, she came into my room, handing me a petri dish. I closed the door behind her, took off my clothes, put on my bathrobe, and went to the bathroom to take a shower. During the shower, I started playing with myself, using the shampoo suds as lube. After rinsing off, I dried off and went back to my room, closed the door, and dropped the bathrobe. Standing naked in front of my desk, over the petri dish, I started to jerk off. It did not take long before I was at full mast. Knowing that the girls knew what I was doing here made it extra hot. My cock was hard as a rock, and the head was dark purple. I slowed down to long and slow strokes because I wanted it to last, but I was almost too late because I felt the tingling feeling of an impending orgasm rise. I let go of my cock and took a few deep breaths to interrupt it.

"Oh, you've already started!"

Tanya stood in the doorway, looking at me. I tried hiding my cock behind my hands, but I knew that she'd probably seen it all. "Don't you knock?"

"Why? After all, we all know what you are doing here!" she laughed. "I just wanted to tell you that the dishes are done, and we are ready for your sample." With that, she closed the door and left me alone. Apparently, my little brain was taking over from my big brain as I got the idea to perform the 'extraction' in my sister's room in front of them instead of in my own room.

I put my bathrobe back on, picked up the petri dish, and went to Kate's room. For a moment, I stood in front of the door, deciding whether or not to wear the bathrobe when going inside. "In for a penny, in for a pound." I thought to myself as I let the robe slip off onto the floor. I grabbed myself to get myself as hard as possible, which only took a few strokes. My heart was pounding in my throat as I opened the door and walked into the room.

The girls shrieked loudly when I walked in stark naked with my cock standing to attention. The shrieks soon made way for clapping and hooting, although Julie was hiding her eyes behind her hands.

"I figured you might want to see how I create your sample... for educational purposes, of course!"

"Of course!" Tanya replied.

Tanya and Kate were sitting on Kate's bed, and Julie was sitting next to the bed on the desk chair. I handed the petri dish to Julie, which made her remove at least one hand from her eyes. A few moments later, she dropped the pretense and dropped her other hand as well. She was now looking directly at my cock, which was just inches away from her face. I grabbed my shaft and made slow, deliberate strokes. Suddenly, I felt a sharp smack on my ass. I turned to my side and saw that Tanya had slapped me.

"Hey, are you giving Julie a private show? How about us?"

I corrected her: "Show? Don't you mean lesson? Educational purposes, remember?" I was still making the same long, slow strokes, but now facing Tanya and Kate.

Kate hadn't said anything yet. She was mesmerized by the spectacle occurring in front of her. I let go of my cock to let her take a good look. Tanya was looking at it from the side, took her chance, and grabbed my cock. She started jerking me. Her fingers felt small compared to my own.

"Don't squeeze too hard," I guided her. "Try slow and long... Oh yeah, just like that. hmmm!... Now, fast and short."

She took my instructions, and I thought that she could have easily let me cum. I stopped her by tapping her hand. I looked my sister in the eye and nodded to her, signaling that it was her turn. She looked at me in disbelief. "Go ahead." I said with a reasuring smile.

My sister hesitantly moved her hand to my cock and traced her fingers along my shaft before slowly folding her fingers around it. She was now looking at the cock in her hand, and studying it a while before she started to masturbate me. Apparently, she had paid attention to what I had said to Tanya. Kate was skillfully jerking me off, slow at first, and steadily picking up pace. Julie was staring at it from the side. I signaled Kate to stop and turned to Julie.

"Your turn," I said. She awkwardly grabbed me with her right hand and started with a slow up-and-down motion. "You can grab a little harder." I told her, which she did. "If you put away the petri dish, you can use your left hand to grab my balls." Without a word, she did just that. "Okay, now speed up a little." She started stroking me faster, and her other hand gently played with my balls. I felt my orgasm approaching again and started to moan while thrusting my hips towards her. Julie responded by stopping her stroke and letting me fuck her hand, which she held still in place.

"I'm about to cum," I announced as I took over the stroking from Julie. "Get the petri dish!" I turned my body a little towards Tanya and Kate to make sure they could see everything. Julie held out the petri dish in front of me while I was facing Tanya. I continued to stroke as my orgasm started to come over me. Now I was grunting rather than moaning. "Oh, fuck. I'm cumming!" My knees buckled, which made it difficult for Julie to hold the petri dish in place. The first stream of cum landed in the dish, but it had so much speed that it bounced out and landed on the bed next to Tanya. The second stream did the same but landed in her hair. I took Julie's hand holding the dish and held it more at an angle so that the following ropes more or less stayed on. More or less, because the dish was now overflowing on Julie's hand. With the last spasms, the final globs of cum came out and slowly dripped down my shaft. The three girls were now looking at my spent but still rigid member, twitching in post-orgasm.

"Wow," my sister exhaled, breaking the silence. "Thank you for that."

"I hope I've given you a good sample." I looked at Julie, who was still holding the dish.

She put the dish on the desk next to the microscope and absentmindedly started licking the spilled cum from her fingers. Tanya, Kate, and I exchanged surprised glances.

"Julie!" Tanya yelled.

"What?" Julie reacted after pulling her finger from her mouth.

Suddenly, she realized what she had been caught doing. And buried her face in her hands, laughing.

"Just leave enough to study under the microscope," Tanya said.

I could only add: "It's going to take me at least 15 minutes before I can give you another sample!"

"Would you do that?" my sister asked. I just smiled at her and walked out of the room, picking up the bathrobe I left at the door.