ANIMAL METAMORPHOSIS. 181 



gnaws through the envelope, and though on emerging the creature 

 is not more than half-an-inch in length, it almost instantaneously 

 stretches out to an inch and a quarter, while its wings, which did 

 not exceed the sixth of an inch, expand to nearly three inches. 



The Goat-moth lives three years in the larval form ; while the 

 larva of the Stag-beetle for several years burrows in the wood of 

 the oak before assuming its perfect form, and flying about among 

 the trees during the summer evenings ; and the larvce of the 

 Tetramera (one of the sections of the Coleoptera) pass a long 

 time in the pupal stage, having been known to eat their way out 

 of wood even after it has been made into furniture. 



Some species of the Ephemerae, after emerging from the pupa, 

 and making use of their wings even for some considerable dis- 

 tance, have yet to undergo another change. Fixing themselves by 

 their claws in a vertical position on some object, they withdraw 

 every part of the body, even the legs and wings, from a thin 

 pellicle, which has enclosed them as a glove does the fingers. 



Having passed in review through the various classes of the 

 Invertebrata, we now come to the second grand division of the 

 animal kingdom — the Vertebrata. It was formerly supposed that, 

 of all the Vertebrata, the Amphibians were the only class that 

 underwent a metamorphosis ; but of late years it has been dis- 

 covered that the young of some of the most lowly organised fishes 

 are so unlike the adult that they were described a's belonging to 

 distinct genera. This is the case with the Lamprey, the young of 

 which, until the discoveries of Auguste ]Muller in 1856, were des- 

 cribed as distinct animals under the name of Animoactes^ and as 

 other forms have never been observed with roe or milt, it is 

 probable that they are the larvae of some larger kinds of fish. 



The young of the Amphibians invariably undergo metamor- 

 phosis after exclusion from the egg, though in some cases the 

 eggs are retained so long in the parent that there is little or no 

 obvious change. In the metamorphosis of the Batrachians we 

 seem to have the process carried on before our eyes to its fullest 

 extent. Not only is one specific form changed to another of the 

 same genus, but we have a transition from one class to another. 

 The fish becomes a frog, the aquatic animal changes to a terres- 

 trial one, the water-breather becomes an air-breather. On its 



