[Lect. III. EAELY LIFE OF A MARSUPIAL. 63 



and the embryo develops rapidly, the cartilage and 

 bone ap]3earing very early. Such is the case in 

 the Lejyidosteus, or Bony Garpike, and in the 

 Sturgeon. 



In these young Kangaroos (an inch long) the ossifi- 

 cation of the skull is much advanced, as I found to my 

 sorrow when sections were made of them by the micro- 

 tome; in young, three-fourths ripe, of the Virginian 

 Opossum, the size of the larva of a Blue-fly (fig. 7, p. Gl), 

 the development was also very advanced, and the 

 cartilage quite solid. There is a considerable amount 

 of contractile or muscular tissue in the teat of the 

 mother, and the structure of the throat of the young 

 is such that the syringing action of the walls of the 

 duct does not choke it, the larynx passing up above 

 the soft palate. There is thus, as in the Cetacea, a 

 direct passage of air from the external nostrils to the 

 glottis (or opening of the windpipe), and fluid can pass 

 rio-ht and left of the breathino; tube, with no dano'er of 

 choking. 



This temporary modification of the young Marsupial 

 to conditions which, for a time, endanger its breathing 

 apparatus, is well worthy of notice, albeit it is but one 

 amid ten thousand instances of the ready response of 

 the organism to the influences by which it is surrounded. 

 Indeed, the earth and the inhabitants thereof, may in 

 some sort he looked at, collectively, as a great, infinitely 

 complex organism, and the working of the whole, as if 



