diff --git a/Runtime/Scripts/MonoBehaviours/WorldBehaviour.cs b/Runtime/Scripts/MonoBehaviours/WorldBehaviour.cs
index be892be..df0d834 100644
--- a/Runtime/Scripts/MonoBehaviours/WorldBehaviour.cs
+++ b/Runtime/Scripts/MonoBehaviours/WorldBehaviour.cs
@@ -103,12 +103,10 @@ private void AddSystemToGroup(ComponentSystemGroup group, ComponentSystemBase sy
             switch (group) {
                 case IList<ComponentSystemBase> lcsg:
                     lcsg.Add(system);
-                    break;
-                case ComponentSystemGroup csg:
-                    csg.AddSystemToUpdateList(system);
-                    break;
+                    return;
                 default:
-                    throw new Exception("Group must be compatible.");
+                    group.AddSystemToUpdateList(system);
+                    return;
             }
         }
     }
diff --git a/Runtime/Scripts/Systems/Groups/ListComponentSystemGroup.cs b/Runtime/Scripts/Systems/Groups/ListComponentSystemGroup.cs
index dc27c6f..8dc61d5 100644
--- a/Runtime/Scripts/Systems/Groups/ListComponentSystemGroup.cs
+++ b/Runtime/Scripts/Systems/Groups/ListComponentSystemGroup.cs
@@ -2,16 +2,30 @@
 using System.Collections;
 using System.Collections.Generic;
 using System.Collections.ObjectModel;
+using System.Reflection;
 using Unity.Entities;
 using UnityEngine;
 
 namespace Software10101.DOTS.Systems.Groups {
+    /// <summary>
+    /// Component system group that acts like a List. Not compatible with unmanaged systems.
+    /// </summary>
     public abstract class ListComponentSystemGroup :
         ComponentSystemGroup,
         IList<ComponentSystemBase>,
         IReadOnlyList<ComponentSystemBase>,
         IList {
 
+        private List<ComponentSystemBase> _underlyingSystemsToUpdate;
+        private static readonly FieldInfo UnderlyingSystemsToUpdateField = typeof(ComponentSystemGroup).GetField(
+            "m_systemsToUpdate",
+            BindingFlags.Instance | BindingFlags.NonPublic);
+
+        private List<ComponentSystemBase> _underlyingSystemsToRemove;
+        private static readonly FieldInfo UnderlyingSystemsToRemoveField = typeof(ComponentSystemGroup).GetField(
+            "m_systemsToRemove",
+            BindingFlags.Instance | BindingFlags.NonPublic);
+
         private ComponentSystemBase[] _systems = new ComponentSystemBase[0];
         private readonly List<ComponentSystemBase> _mutableSystemsList = new List<ComponentSystemBase>();
         private bool _systemsListDirtyFlag = false;
@@ -24,12 +38,39 @@ public abstract class ListComponentSystemGroup :
 
         public override IEnumerable<ComponentSystemBase> Systems => _systems;
 
+        protected override void OnCreate() {
+            _underlyingSystemsToUpdate = (List<ComponentSystemBase>)UnderlyingSystemsToUpdateField.GetValue(this);
+            _underlyingSystemsToRemove = (List<ComponentSystemBase>)UnderlyingSystemsToRemoveField.GetValue(this);
+        }
+
         protected override void OnUpdate() {
+            if (_underlyingSystemsToUpdate.Count > 0) {
+                _mutableSystemsList.AddRange(_underlyingSystemsToUpdate);
+                _underlyingSystemsToUpdate.Clear();
+                _systemsListDirtyFlag = true;
+            }
+
+            if (_underlyingSystemsToRemove.Count > 0) {
+                _underlyingSystemsToRemove.ForEach(system => _mutableSystemsList.Remove(system));
+                _underlyingSystemsToRemove.Clear();
+                _systemsListDirtyFlag = true;
+            }
+
             if (_systemsListDirtyFlag) {
                 _systemsListDirtyFlag = false;
                 _systems = _mutableSystemsList.ToArray();
             }
 
+            if (UpdateCallback == null) {
+                UpdateAllSystems();
+            } else {
+                while (UpdateCallback(this)) {
+                    UpdateAllSystems();
+                }
+            }
+        }
+
+        private void UpdateAllSystems() {
             int count = _systems.Length;
             int index;
 
diff --git a/package.json b/package.json
index 4431b7b..f00818e 100644
--- a/package.json
+++ b/package.json
@@ -1,7 +1,7 @@
 {
   "name": "com.10101software.dots.hybridsimulation",
   "description": "A framework for using FixedUpdate in a simulation world which is linked to a GameObject-based presentation layer.",
-  "version": "0.4.0",
+  "version": "0.4.1",
   "unity": "2020.1",
   "displayName": "DOTS Hybrid Simulation Worlds",
   "dependencies": {