THE ANIMAL KINGDOM 19 



we can only guess at. To find the reason is rather 

 the province of the student of variation and heredity ; 

 it is our task to show that it is so. The special 

 importance which attaches to such animals is that 

 they enable us to see relationships between modern 

 groups which have undergone rapid and far-reaching 

 changes, and whose connection with one another and 

 with other forms would be obscured were it not 

 for the existence of these ancient, connectant or 

 primitive types. 



We shall also deal shortly with the young de- 

 velopmental stages of certain animals, which as 

 adults do not particularly betray their affinities, but 

 which during development pass through stages of the 

 greatest significance in revealing their nature and 

 relationship. 



Finally our attention may be attracted to animals 

 that are on the threshold of, or have recently suffered, 

 extinction, and here the link is not so much with the 

 ancient past of animal life, as with that more tangible 

 past when man had already begun to exercise 

 dominion over the earth and to exert that immense 

 influence over living creation the final effects of which 

 are still to be witnessed. 



22 



