3.5 HD increase for Druid AC

[Shocksrivers]

Hi everyone,

my first attempt at a Druid after a few years of playing, but I keep getting confused by the Animal Companion.
The main issue right now is: Am I correct in thinking the size of a wolf goes up from medium to large at 4 HD, meaning that I should consult the MonsterManual I, page 291, for the table on size increases following from HD increase? And that the wolfs strength goes up by 8?

[ksbsnowowl]

No, the animal companion is not advancing normally as a "wolf" or whatever the base animal is. It is advancing via the druid class feature. It gains HD and everything that comes with HD, but it does not ever increase in size.

[Nifft]

Animal companions gain bonus HD, but they're not improving as natural creatures would.

You get only the listed benefits -- which don't include any size increases.

[Shocksrivers]

Thank you!

So I only use whatever is on page 36 of the PHB?

[Kaleph]

Yes, don't forget to assign your animal companion skill ranks (arguably 1/level) and feats.

Also, you may want to change your companion from time to time, so you can get larger, thougher monsters.