84 REPTILIAN WATER TRESPASSERS. 



perceptible from day to day in their external form, 

 they acquire a tenfold interest to the physiologist who 

 traces the progressive evolution of their internal viscera. 

 More especially, when he finds that in these creatures 

 he has an opportunity afforded him of contemplating, 

 displayed before his eyes, as it were, upon an enlarged 

 scale, those phases of development through which the 

 embryo of every air-breathing vertebrated animal must 

 pass while concealed within the egg. 



" The division, therefore, of reptiles into such as 

 undergo a metamorphosis and such as do not, is by no 

 means philosophical, though convenient to the physio- 

 logist ; for all reptiles undergo a metamorphosis, though 

 not to the same extent." 



Mr. Jones then proceeds to sum up the subject by 

 showing that in the Perennibranchiate reptiles the 

 change from the aquatic to the air-breathing animal is 

 never fully accomplished, while in the Caducibranchiates 

 the change takes place after the young has been 

 hatched. He then shows that even in the case of the 

 reptiles proper, such as the lizards, snakes, and 

 tortoises, a similar change takes place, though it is 

 accomplished within tKe egg, long before the little 

 animal is hatched. And the same rule holds good with 

 birds. 



From these observations the reader will, I think, 

 see the extreme value, not only of observation, but of 

 generalizing the facts that are observed. 



Even if taken alone, the faculty of observation is of 

 very high value. It adds a new charm to life, and 

 gives entrance, so to speak, into a different world. 

 The good old story of "Eyes and No Eyes" is applicable 



