trying to make a nested collection

sentence.js

window.show = function(o){ return JSON.stringify(o, null,2)}

app = {}; 

app.Word = Backbone.Model.extend({
})

app.Words = Backbone.Collection.extend({
  model: app.Word,
  localStorage : new Backbone.LocalStorage('srsly_words')
})

app.Sentence = Backbone.Model.extend({
  initialize: function(){ 
    this.set({'words': new app.Words});
  },  
  url : 'js/sentence_data.js',
  parse: function(response){ 
    this.get('words').reset(response.words);
    return response;
  }
})

app.Text = Backbone.Collection.extend({
  model: app.Sentence,
  localStorage : new Backbone.LocalStorage('srsly_text'),

})

$(function(){

  app.sentence = new app.Sentence();

})

sentence_data.js

{
  "transcription": "hinispleʔ eč ašup, siyamš aʔoʔ",
  "translation": "When this world perished, it was full of water",
  "words": [
    { "morphemes" : "hini-s-pleʔ", "gloss" : "when-3RD-SG-to.perish" }, 
    { "morphemes" : "eč", "gloss" : "this" }, 
    { "morphemes" : "ašup", "gloss" : "world" }, 
    { "morphemes" : "s-iyam-š", "gloss" : "3RD.SG-to.be.full-INTR"      }, 
    { "morphemes" : "aʔoʔ", "gloss" : "water"       }  
  ]
}