180 ARTHROPODA 



larger shells and watch the crabs test them to determine 

 which will serve best. 

 A drawing is desirable. 



Thompson: The Metamorphoses of the Hermit Crab. Proc. Bost. Soc. 

 Nat. Hist., 31, 1903. 



EMERITA (Sand Mole) 



On sand beaches, between low- and high-water mark, 

 there may frequently be seen the shallow depressions that 

 mark the places where these animals have burrowed. They 

 may be dug out with a shovel, but they quickly disappear 

 again. 



1. Notice their shape and the ease and rapidity with 

 which they burrow. 



2. Place specimens in a dish containing sand and a little 

 sea water and try to determine just how the burrowing is 

 done. This may frequently be done by holding a specimen 

 so it just touches the sand. Which end goes into the sand first? 

 Notice the positions in which the appendages are held. Does 

 this have anything to do with the direction in which it bur- 

 rows? Does the animal jump or crawl? In what direction 

 and how can it swim? 



3. Examine the body and see if it is divided into head, 

 thorax, and abdomen. In what way is the shape of the telson 

 adapted to its function? 



4. Examine the appendages. 



(a) The stalked eyes. 



(b) The biramous first antennae and the exceedingly long, 

 feathery second antennae. What is the usual position of the 

 antennae? 



(c) The mouth appendages. Are strong, hard mandibles 

 present? What must the character of the food be? 



(d) The thoracic appendages. How many are there? 

 Are they similar? Are there any chelae? 



(e) The abdominal appendages. Are they all alike? 

 What functions are performed by them? 



Make a drawing. 



