120 



ZOOLOGY 



when an antenna will regenerate (Fig. 117), one or two 

 extra oviducts may occur, or double monsters sort of 



Siamese twins - - may be hatched 

 out. Similar monstrosities are 

 found in other arthropods. 



Physiological Division of Labor. 

 The difference between a 

 " highly developed " animal and a 

 lowly organized one is not first 

 of all a difference of size nor a 

 difference in the number of parts, 

 - just as a large population or 

 numerous cities are not the pri- 

 mary characteristics of a highly 

 civilized state. But just as a 

 complex civilization is one in 

 which each of the different citizens 

 has his own special task to per- 

 form for the commonwealth, so 

 a highly developed organism is 

 one in which each different o reran 



o 



has its special role to play. The 

 worm Nereis has more segments 



o 



to the body than the crayfish, but 

 these segments are very nearly 

 alike the parapodia especially 



FIG. lib. Two abnormal claws. J 



Upper figure shows a double are quite similar. In the crayfish, 



CrCethe r ^TextS " the other hand, the append- 

 finger. From Herrk-k. ages are dissimilar. Each pair 



has a special function to perform 



and is specially adapted, often complexly fashioned, to 

 meet this need. What is true of the appendages is like- 



