diff --git a/1-base/lace/source/events/interface/lace-observer.ads b/1-base/lace/source/events/interface/lace-observer.ads
index 4c9b8bf..d7d357b 100644
--- a/1-base/lace/source/events/interface/lace-observer.ads
+++ b/1-base/lace/source/events/interface/lace-observer.ads
@@ -49,7 +49,7 @@ is
    -- Operations
    --
 
-   procedure receive (Self : access Item;   the_Event    : in Event.item'Class := event.null_Event;
+   procedure receive (Self : access Item;   the_Event    : in Event.item'Class;
                                             from_Subject : in event.subject_Name) is abstract;
    --
    -- Accepts an Event from a Subject.
diff --git a/1-base/lace/source/events/interface/lace-subject.ads b/1-base/lace/source/events/interface/lace-subject.ads
index b10c119..f430d7a 100644
--- a/1-base/lace/source/events/interface/lace-subject.ads
+++ b/1-base/lace/source/events/interface/lace-subject.ads
@@ -61,11 +61,11 @@ is
    -- Emit
    --
 
-   procedure emit (Self : access Item;   the_Event : in Event.item'Class := Event.null_Event) is abstract;
+   procedure emit (Self : access Item;   the_Event : in Event.item'Class) is abstract;
    --
    -- Communication errors are ignored.
 
-   function  emit (Self : access Item;   the_Event : in Event.item'Class := Event.null_Event)
+   function  emit (Self : access Item;   the_Event : in Event.item'Class)
                    return Observer_views is abstract;
    --
    -- Observers who cannot be communicated with are returned.
diff --git a/1-base/lace/source/events/lace-event.ads b/1-base/lace/source/events/lace-event.ads
index 8ada8f1..6fc45c0 100644
--- a/1-base/lace/source/events/lace-event.ads
+++ b/1-base/lace/source/events/lace-event.ads
@@ -9,9 +9,7 @@ package lace.Event
 is
    pragma Pure;
 
-   type Item is tagged null record;
-
-   null_Event : constant Event.item;
+   type Item is tagged private;
 
 
    subtype  subject_Name is String;
@@ -35,5 +33,13 @@ is
 
 
 private
-   null_Event : constant Event.item := (others => <>);
+
+   type sequence_Id is range 0 .. 2**32 - 1;
+
+
+   type Item is tagged
+      record
+         s_Id : sequence_Id;
+      end record;
+
 end lace.Event;
diff --git a/1-base/lace/source/events/mixin/lace-make_observer.adb b/1-base/lace/source/events/mixin/lace-make_observer.adb
index b6a99d5..22d89bf 100644
--- a/1-base/lace/source/events/mixin/lace-make_observer.adb
+++ b/1-base/lace/source/events/mixin/lace-make_observer.adb
@@ -63,7 +63,7 @@ is
    --
 
    overriding
-   procedure receive (Self : access Item;   the_Event    : in Event.item'Class := Event.null_Event;
+   procedure receive (Self : access Item;   the_Event    : in Event.item'Class;
                                             from_Subject : in Event.subject_Name)
    is
    begin
@@ -184,7 +184,7 @@ is
       --
 
       procedure receive (Self         : access Item'Class;
-                         the_Event    : in     Event.item'Class := Event.null_Event;
+                         the_Event    : in     Event.item'Class;
                          from_Subject : in     Event.subject_Name)
       is
          use event_response_Maps,
diff --git a/1-base/lace/source/events/mixin/lace-make_observer.ads b/1-base/lace/source/events/mixin/lace-make_observer.ads
index dfee279..4dad8f7 100644
--- a/1-base/lace/source/events/mixin/lace-make_observer.ads
+++ b/1-base/lace/source/events/mixin/lace-make_observer.ads
@@ -48,7 +48,7 @@ is
    --
 
    overriding
-   procedure receive (Self : access Item;   the_Event    : in Event.item'Class := event.null_Event;
+   procedure receive (Self : access Item;   the_Event    : in Event.item'Class;
                                             from_Subject : in Event.subject_Name);
    overriding
    procedure respond (Self : access Item);
@@ -120,7 +120,7 @@ private
       --
 
       procedure receive (Self         : access Item'Class;
-                         the_Event    : in     Event.item'Class := Event.null_Event;
+                         the_Event    : in     Event.item'Class;
                          from_Subject : in     Event.subject_Name);
 
    private
diff --git a/1-base/lace/source/events/mixin/lace-make_subject.adb b/1-base/lace/source/events/mixin/lace-make_subject.adb
index 2105a41..4501e23 100644
--- a/1-base/lace/source/events/mixin/lace-make_subject.adb
+++ b/1-base/lace/source/events/mixin/lace-make_subject.adb
@@ -102,7 +102,7 @@ is
 
 
    overriding
-   procedure emit (Self : access Item;   the_Event : in Event.item'Class := Event.null_Event)
+   procedure emit (Self : access Item;   the_Event : in Event.item'Class)
    is
    begin
       if Self.Emitter = null
@@ -145,7 +145,7 @@ is
 
 
    overriding
-   function emit (Self : access Item;   the_Event : in Event.item'Class := Event.null_Event)
+   function emit (Self : access Item;   the_Event : in Event.item'Class)
                   return subject.Observer_views
    is
       use lace.Event.utility;
diff --git a/1-base/lace/source/events/mixin/lace-make_subject.ads b/1-base/lace/source/events/mixin/lace-make_subject.ads
index 7418f02..a5243ae 100644
--- a/1-base/lace/source/events/mixin/lace-make_subject.ads
+++ b/1-base/lace/source/events/mixin/lace-make_subject.ads
@@ -59,10 +59,10 @@ is
    --
 
    overriding
-   procedure emit (Self : access Item;   the_Event : in Event.item'Class := Event.null_Event);     -- TODO: Rid default.
+   procedure emit (Self : access Item;   the_Event : in Event.item'Class);
 
    overriding
-   function  emit (Self : access Item;   the_Event : in Event.item'Class := Event.null_Event)      -- TODO: Rid default.
+   function  emit (Self : access Item;   the_Event : in Event.item'Class)
                    return subject.Observer_views;
 
    overriding
@@ -109,8 +109,8 @@ private
 
 
 
-   -----------------
-   -- Safe observers
+   ------------------
+   -- Safe observers.
    --
    protected
    type safe_Observers
@@ -132,10 +132,9 @@ private
 
 
 
-   ---------------
-   -- Subject Item
+   ----------------
+   -- Subject Item.
    --
-
    type event_Emitter_view is access all event_Emitter.item'Class;
    type event_Sender_view  is access all event_Sender .item'Class;
 
diff --git a/1-base/lace/source/events/mixin/xgc/lace-make_observer-deferred.adb b/1-base/lace/source/events/mixin/xgc/lace-make_observer-deferred.adb
index 8fee071..e95ed47 100644
--- a/1-base/lace/source/events/mixin/xgc/lace-make_observer-deferred.adb
+++ b/1-base/lace/source/events/mixin/xgc/lace-make_observer-deferred.adb
@@ -23,7 +23,7 @@ is
    --
 
    overriding
-   procedure receive (Self : access Item;   the_Event    : in Event.item'Class := Event.null_Event;
+   procedure receive (Self : access Item;   the_Event    : in Event.item'Class;
                                             from_Subject : in Event.subject_Name)
    is
    begin
diff --git a/1-base/lace/source/events/mixin/xgc/lace-make_observer-deferred.ads b/1-base/lace/source/events/mixin/xgc/lace-make_observer-deferred.ads
index 4b755fd..07aa98a 100644
--- a/1-base/lace/source/events/mixin/xgc/lace-make_observer-deferred.ads
+++ b/1-base/lace/source/events/mixin/xgc/lace-make_observer-deferred.ads
@@ -31,7 +31,7 @@ is
    --
 
    overriding
-   procedure receive (Self : access Item;   the_Event    : in Event.item'Class := Event.null_Event;
+   procedure receive (Self : access Item;   the_Event    : in Event.item'Class;
                                             from_Subject : in Event.subject_Name);
    overriding
    procedure respond (Self : access Item);