In chapter five of "Lord of the Flies", why does Piggy show disapproval when Ralph calls his assembly?

Piggy's disapproval does not stem from Ralph having called the meeting, but rather, how the meeting is conducted and what is being discussed at the meeting.  Piggy is the "brains" of the group of boys; he represents the intellectual and as such, he is upset that the meetings are not conducted the way they should be so that things could be accomplished.  The "conch shell rule" of letting whoever holds the shell speak is not being enforced. The meetings are often broken up by silliness and therefore little is done.  At this particular meeting, the topic is whether or not there are beasts.  Piggy wants to show how illogical the notion is.  He also suggests that what the boys have to fear is their own savagery which is corroborated by Simon.   This meeting, like so many others, ends in chaos.  Life is becoming more and more chaotic on the island and Piggy realizes this.  He knows that having some place where rules are enforced will help slow this trend and he thinks the meetings are one of those places where there should be order.