As many of you maybe know Spot changed somewhere in the show from a male to a
female cat. Below you can find a story which can be a explanation of how this happened.
It was written by Olivia Adler from Germany and published here with permission.
It was posted before in one of the Star Trek newsgroups.

Copyright notice: Star Trek, The Next Generation, and all related characters, are trademark and property of Paramount. However, the story I borrowed their universe for is mine. This little piece of writing which you shouldn't take too serious (and of course you don't) will solve one of the riddles the "Next Generation" series gave us: the miraculous transformation inappearance and gender of Spot, Data's beloved cat. Be prepared for innuendoes ;).
The Search for Spot
 Data thoughtfully watched his cat, Spot, who was bathing on the floor of their common quarters. Although the second officer of the "Enterprise D" was an android and therefore unable to feel, he did consider his animal companion rather as an individual and a friend than a representative of the species "felis domestica", a Somali cat in this particular case. Spot nourished his continual curiosity day by day, and during his intensive research in the field of human experiences and behavior Data had learned that cats had been riddles and secrets for humans during all times - and never predictable. The former was a permanent challenge for the android who still tried to categorize Spot's behavior in a logical manner which would enable him to determine the cat's actions. So far, all attempts in that direction had failed.
When Data looked into the yellow, mysterious cat eyes, sometimes he had the impression as if he was facing a related soul. He did not know how to describe the phenomenon, since he had not found a scientific explanation yet. And his positronic brain didn't have any use for vague ideas.
"Sometimes I tend to believe that you understand every word I say", Data said and reached out for his violin. "Human beings always have dreamed of being able to talk to the animals. Until today, this dream has not been fulfilled. If I were a human being, I would regret that." Data tried a melancholy expression - which was not really difficult, since this was quite close to his usual facial expression - and started playing an ancient Scottish melody. Spot tilted his head, listened closely for a moment, decided that the presentation was acceptable and cuddled up.

 "Sure, I can watch Spot while you're away", Geordi LaForge said. "When will you return from your research mission?"
"The Enterprise will pick me up in one week", Data said. "I am really grateful that you will care for Spot. He is rather selective in the choice of his food, and he needs a great deal of attention. The first thing..."
"Data", the Chief Engineer of the Enterprise interrupted him, "I know how to handle cats. And it has been more than once that you informed me about Spot's habits. Don't worry. Everything will be fine."

"Damned!" Geordi swore. "Spot, where are you? No more silly jokes! Come out here!"
He knew that this was useless. He already had searched through Data's whole quarters. Apparently Spot had escaped, like he had done so many times before. Data's animal friend was a real master in that skill. Geordi sighed and touched his comm badge. "LaForge to Worf. Can you spare some time?
I have a little problem here..."
"I knew it", LaForge sighed. "I shouldn't have started with it. He's totally disappeared. And we really didn't overlook anything?"
Worf grimly shook his head. "We have searched everything. The cat of Lt. Cmdr. Data is apparently not on the ship anymore."
"That's impossible!" Geordi protested. "Unless..."

"Unless the animal is dead", the Klingon Security Officer dryly finished the sentence.
Geordi already wanted to start answering, but he was interrupted with the chirping of the comm badge. "Commander LaForge?"
"Yes, Ensign?"
"We have found the cat - in one of the cargo bays. She came too close to a plasma conduit. Um... Commander - she doesn't look good."
"Great. Just great", LaForge muttered. "Thank you, Ensign. I'll take care of it."

 "I'm sorry, Geordi", Beverly Crusher regretted. "There's nothing I can do for him."
The dead cat presented a miserable sight. Although he knew it better, LaForge had brought Spot into sickbay, in the irrational hope that he could be saved. The ship's doctor had confirmed his fears.
"But there must be another Somali cat on the ship!"
"Negative", the calm voice of the ship's computer said. "Currently there are 23 specimens of the species "felis domestica" on board, but none that would fit the required specification."

"So much for this", Geordi sighed. "LaForge to Lieutenant Barclay!"
"Barclay here", the answer came from the communicator.
"Barclay, I need your help. We have a minor problem here..."

"I... I am not sure", Barclay stammered. "You want to use the transporter to replicate a cat like Spot?"
"If possible, yes", LaForge said unhappily. "But we don't have a pattern of Spot stored. The question is: has there ever been a transport of a cat, and is there a chance we could modify the equipment in a way that would enable us to replicate a Somali cat?"
Barclay's facial expression clearly revealed what he thought of the idea, but he hesitated to tell it.
Two days later LaForge gave up. The results of the replication had not been satisfactory. Although they finally had been able to replicate the body of a Somali cat, it still was dead matter. He hadn't really expected a success, but he did not want to face his best friend without having tried everything.
"You... you shouldn't hold that against yourself", Barclay tried to soothe him. "Nobody could have prevented it, even not Commander Data. He won't hold it against you."
LaForge sighed again. Barclay wasn't exactly cut out to foresee the reactions of his fellow creatures. "Barclay...?"
"Yes, Sir?"
"Are you familiar with Cybernetics?"
"A little... Why?"
"We have one possibility left."
On the experimental table there was a small body with long, silky, cream colored fur. It was a robotic replica of Spot. The cat looked perfect - apart from one flaw: It didn't work the way it was supposed to. LaForge and Barclay had managed to construct a functioning robot, but the result was unsatisfactory.
"Let's try it once more", LaForge said, ignoring Barclay's skeptical look, and switched on the cat.
The animal stretched its body, meowed ('I have to change the amplitude', LaForge thought. 'It doesn't sound right'), jumped down the table - and failed. The smell of smouldering circuits filled the air.
"No way", LaForge decided. "We don't have enough time until Data returns. I'm afraid I'll have to tell him the truth."
"What's so bad about that?" Barclay asked innocently. "It was a tragic accident - but Lt. Commander Data doesn't have feelings. He will understand it."
Although covered by the VISOR, the look LaForge threw at him created the irresistible need in Barclay to immediately retire to the familiar shelter of the holodeck. "I wouldn't be so sure about that..."

 "Come in", the warm, calm voice of the Counselor said. Geordi kicked himself and entered Deanna Troi's treatment room. "I need your advice", he came right to the point. "I'm sure you have heard what happened to Data's cat."
The Betazoid nodded. "A sad story."
"I've let him escape", LaForge said unhappily. "It's my fault. And I know how much Spot meant to Data. What shall I do now? I have already tried almost anything: the transporter, a robotic replica... and we don't have another Somali cat on board. I've run out of ideas. Data will never forgive me..."
"Don't be so angry with yourself", Deanna soothed him. "We all know that Spot had an amazing talent for escaping Data's quarters. I have also been thinking about it, and I may have an idea..."
Data wondered why LaForge was not around when he returned. "Where is Commander LaForge?" he asked the Transporter Chief.
"As far as I know, he wanted to wait for you in your quarters."
Data tilted his head, as he did most of the time when he was trying to understand something. Then he shrugged and went to his quarters.
The door slid back. LaForge stood up from the chair where he had been waiting. In his arms he held a red striped domestic cat. "Data! Welcome home!" The joy in his dark face vanished and changed into sudden concern when he became aware of Data's searching look. "Um... I have to tell you something... concerning Spot..."
"I do not see Spot", Data simply stated. "Where is he?"
"Oh well..." Finally, Geordi told the whole story. "We have tried everything", he finished, "even a robotic replica. Nothing helped. In the end Counselor Troi had another idea..." He threw a helpless look at the cat in his arms which was becoming impatient now. He put down the wiggling animal. The cat took a few steps towards Data and mewled.
Data kneeled down and examined the cat carefully. The cat examined Data. Geordi had the impression as if they both were communicating on a level he couldn't access. The yellow eyes of the cat resembled his friend's in an amazing way. Finally, Data took the cat into his arms. She started purring.
A fine smile appeared on the android's gentle face. "Hello... Spot."

Outside, on the exterior hull of the ship, stood a lone figure, wrapped in a long coat. "Mais oui, Monsieur android", Q mused, "sometimes thou understandeth more than thy human friends do. However, I must ask myself how long thou wilt need until thou discovereth that this Spot actually is a female." His aristocratic features twisted into a malicious smile. "And this shalt save thy lives one day - MON CAPITAN."
In his quarters, Captain Picard startled from his deep sleep. A strange dream had wakened him. For a moment he tried to remember, then he shook his head in annoyance. "Nonsense. A cat that changes into an iguana!" With that, the dream was forgotten.

(c) oladler@aol.com (Olivia Adler) October 1996