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 organ 

 has its special r61e to play. The 

 worm Nereis has more segments 

 to the body than the crayfish, but 

 these segments are very nearly 



FIG. 116,-Two abnormal claws, alike the parapodia especially 

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



to^^rthere^extS on the other hand > the append- 

 finger. From Herrick. 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- 



