70 



NATURE STUDY REVIEW 



[9 :3— Mar., 1913 



Figure 1. — The Isopod, 

 Ascllus communis $ X 4. 



Figure 2. — The Isopod, 

 Mancasellus Danielsii. 

 (After Richardson. ) 

 X 3%. 



ISOPODS. 



Isopods (Fig. 1 and 2) are commonly known as "sow bugs'" 

 or "pill bugs." The land representatives of the group are quite 

 common and are usually known, since they occur in damp cellars, 

 in green houses or under damp boards. Water isopods resemble 

 their land relatives in a general way and will be immediately 

 recognized if one is acquainted with the land isopods. The name 

 "sow bugs" comes from the fact that the female deposits her 

 eggs in a brood pouch on the under side of the thorax. This 

 pouch often gets so large that the animals are scarcely able to 

 walk. Here the young hatch and are carried until they are about 

 one twenty-fifth of an inch long, when they are liberated as 

 small white animals much like their parent in essential features. 

 Usually about forty young are liberated at a time, although two 

 hundred have been taken from a single brood pouch. Isopods 

 are called "pill bugs" because, in common with amphipods. and 

 many other animals, they have the habit of rolling into a "pill" 

 when disturbed and lying quietly until the eflfect of the shock 

 wears away. 



Isopods are flattened as if a weight had been placed on their 

 backs. The thorax (Fig. 1) bears seven pairs of legs that are 

 very similar and hence the name iso-pod, meaning like — or similar 

 — footed. 



