THE ANIMAL KINGDOM 85 



structure was taken into account for the same pur- 

 pose. At the present time, however, and ever since 

 the doctrine of descent began to be accepted, nat- 

 uralists have had a better criterion for determining 

 relationships. Animals exhibit relationships because 

 they have sprung from a common stock. The mem- 

 bers of a natural group resemble each other in struc- 

 ture because they have a genetic relationship and 

 those that are closest allied have a closer kinship. 

 When the entire animal series is spoken of as the 

 Animal Kingdom, the large natural subdivisions of 

 the territory formerly were called subkingdoms, but, 

 at present, the designation commonly employed for 

 each subdivision is Phylum (from the Greek phylos, 

 a tribe). There is no agreement among zoologists as 

 to the number of phyla into which the animal king- 

 dom should be divided. " Some authorities recognize 

 only eight, while others maintain that there should 

 be as many as twenty or even more." Such extensive 

 subdivision of even the primary groups is probably 

 justified on technical grounds, but, as Richard 

 Hertwig has remarked: "In this way groups poor in 

 species and of little importance in a general account 

 of the animal kingdom are placed on the same basis 

 as the large and exceedingly important groups of 



