142 THE BIOLOGY OF THE ANIMAL 



1. The protopodite (basal portion). — Of how many 



joints does it consist? How are they connected? 

 Of what is the protopodite composed ? Note 



2. The exopodite, attached to the outer margin of 



1, and 



3. The endopodite, attached to the inner margin of 



1. — What is their shape ? Structure ? Color ? 

 Do they show any indications of segmentation? 

 How are they joined to 1 ? 



Compare the first, second, fourth, and fifth 

 abdominal segments with the third in all re- 

 spects. Do you find any noticeable variations 

 in shape, size, general structure, appendages, 

 etc. ? Do you find that all of the appendages 

 are constructed upon the same general plan — 

 *'. e., a basal portion bearing two branches ? In 

 other words, are the appendages homologous ? 

 Draw the third abdominal segment and its append- 

 ages as seen from the end. Draw one of the append- 

 ages, showing its parts. 



Examine next, 



II. The cephalothorax. — What is its shape as seen 

 from above ? From the side ? Note the covering 

 or carapace. Does it show any traces of segmen- 

 tation ? Does it entirely cover the cephalothorax ? 

 At what points is it attached to the body ? What 

 is the structure of its posterior and lateral mar- 

 gins? Examine the cervical groove running 

 across the carapace. What course does it follow ? 

 Note that it divides the carapace into an ante- 

 rior or cephalic and a posterior or thoracic re- 

 gion. Note also the two branchio - cardiac 

 grooves running backward from the cervical 



