82 MAN AND THE LOWER ANIMALS n 



application, that every living creature commences 

 its existence -under a form different from, and 

 simpler than, that which it eventually attains. 



The oak is a more complex thing than the 

 little rudimentary plant contained in the acorn ; 

 the caterpillar is more complex than the egg; 

 the butterfly than, the caterpillar; and each of 

 these beings, in passing from its rudimentary to 

 its perfect condition, runs tt .rough a series of 

 changes, the sum of which is called its Develop- 

 ment. In the higher animals these changes are 

 extremely complicated ; but, within the last half 

 century, the labours of such men as Von Baer, 

 Rathke, Reich ert, Bischoff, and Remak, have 

 almost completely unravelled them, so that the 

 successive stages of development which are ex- 

 hibited by a Dog, for example, are now as well 

 known to the embryologist as are the steps of the 

 metamorphosis of the silk-worm moth to the 

 school-boy. It will be useful to consider with 

 attention the nature and the order of the stages 

 of canine development, as an example of the 

 process in the higher animals generally. 



The dog, like all animals, save the very lowest 

 (and further inquiries may not improbably remove 

 the apparent exception), commences its existence 

 as an egg : as a body which is, in every sense, as 

 much an egg as that of a hen, but is devoid 

 of that accumulation of nutritive matter which 

 confers upon the bird's egg its exceptional size and 



