Is this considered normal behavior when introducing a new kitten to my resident cat?

[Jenny Nelson]

Well! I am absolutely a scared cat mother. My resident cat Louie, who is 6 months, is NOT happy with the new kitten Lily (2 months) to have invaded HIS space! I have Lily in her pet porter and placed on the floor in the living room, Louie is roaming around freely and keeps walking up to Lily's porter and hissing at her. Last night we left the door open a little bit and Louie hopped near the door, hissed, and swatted at the new kitten. I quickly put an end to it and scolded Louie. I'm not giving Lily any attention, not even paying attention to her when she's out in her porter around Louie. When I was petting Louie earlier tonight he started doing a low meow like he was agitated with me, although he was laying on me and letting me pet him. I really don't want to get rid of Lily as she is ADORABLE and I really don't want Louie to be a mean-old cat.
Lily has only been in the house for a little over 24 hours. Am I unnecessarily over-reacting or is this just a bad sign? I want Lily to be able to come out of her pet porter, but I'm so scared that something horrible will happen and I wont be able to get them apart.
Help!?