The_Giant_Mantis said:
Several generations (I think 4, as grey said) into the genestealer life cycle, the cult will produce a magus. Genestealers are programmed to do this.
A magus is a psychically gifted genestealer hybrid capable of channelling some of the majesty of the hivemind. He's also a powerful beacon to hive fleets, as he shows a genestealer cult is growing and prospering.
So basically what grey said.
That list is odd though.. doesn't read like a 3rd/4th ed 40k list.. too complex, and too many special rules and exceptions.
Edit: I've suddenly realised how confusing this post is, because there is also a chaos character for inquisitor called Magnus. Which did you mean?
Yeah, that list isn't a good example, just the first thing I happened to find when I did a search. Basically you've got....
Phase #1

atriarch and perhaps other purestrain genestealers come into contact with host species, perhaps due to landing on new planet, perhaps due to encounter on space hulk, whatever. Patriarch and purestrains implant their seed in the host species using their ovipositors. Ewww.
Phase #2. First generation genestealers are born from host species. Due to either changes in body chemistry or the genestealers hypnotic powers, the parents are slavishly loyal to their children and will protect them at any cost. First generation genestealers go on to infect more members of the host species. Secrecy is paramount at this point since the cult is small and the first generation still look quite alien.
Phase #3. Second and later third generation genstealers are born. Tend to have many more physical and mental characteristics of the host species by this point, often including an ability to take advantage of the host species technology. Still retain the hypnotic abilities common to all genestealers. The cult, with its emphasis on protecting 'children' and a coming golden age grows larger and stronger. The cults 'blood brothers', ie: the hosts species members of the cult often are chosen members of the planets military or civillian government infrastructure.
Phase #4. The fourth generation hybrids are born which can pass as the host species and the true process of infiltration is begun. The fourth generation hybrids(which include the
Magus) can only reproduce by sexual means, their ovipositors no longer being available.
Phase #5. New purestrains are born from the fourth generation hybrids activities.(Don't ask me how they went from being mostly host species back to pure, it doesn't make sense to me either.) By this point the cult will probably engage in open warfare for control of the planet. If successful, we go onto...
Phase #6. If the Tyrannids have not shown up yet to eat the planet, or the host species hasn't wiped them out, the genestealer cult now sends its seed back into space, often having the host species members of the cult build ships with life support chambers to accomplish this. However, even with these, often only the purestrains are still alive bythe time they reach a new breeding ground, so the process starts all over.