Larger Brood
At 8th level, the broodmaster can spend 4 evolution points from the evolution pool for the large evolution; unlike with other evolutions, he spends these 4 points before he assigns evolution points to his individual eidolons (for an 8th-level broodmaster with 11 evolution points, this leaves 7 evolution points to distribute among the eidolons). This allows him to summon two Medium eidolons, four Small eidolons, or one Medium eidolon and two Small eidolons.
At 13th level, if the broodmaster has purchased the large evolution for his brood, he can spend an additional 6 evolution points from the evolution pool for the huge evolution, distributing the remaining points among his eidolons. This allows him to call two Large eidolons, four Medium eidolons, eight Small eidolons, or any similar combination in which two smaller eidolons count as one eidolon of one size larger.