package PClass1;
use strict;
use Carp;

sub new {
    my $proto = shift;
    my $class = ref($proto) || $proto;
    my (%args) = @_;
    my $this = {
	_fs => $args{fs} || croak("You must supply a filesystem"),
    };
    bless $this, $class;
    return $this;
}


...

package PClass2;
use strict;

sub new {
    my $proto = shift;
    my $class = ref($proto) || $proto;
    my (%args) = @_;
    my $this = {
	_hosts => $args{hosts},
    };
    bless $this, $class;
    return $this;
}

......

package Subclass;
use strict;
use PClass1;
use PClass2;
our @ISA=qw(PClass1 PClass2);

sub new {
    my ($class, %args) = @_;
    my $this = {};
    bless $this, $class;
    $this = $class->PClass1::new(%args);
    #HOW DO I CALL THE SECOND CONSTRUCTOR HERE?????
    $this->init($this);
    return $this;
}