130 THE CEAYFISH 



an epipodite, "which may be a simple plate or may be modified 

 to form a gill. From such a typical form aU the appendages 

 of the crayfish can be derived by variations in form and 

 relative size of the various parts, or by total suppression of 

 one or more parts. 



In the following description the appendages are numbered 

 from before backwards, and are distinguished by the large 

 Eoman numerals I. to XIX. 



Bemove the appendages of the right side one by one, 

 beginning with the hindmost, and tahing special care to 

 remove each appendage entire. The characters of the smaller 

 ones can be best made out by examination in a drop of water, 

 between two slips of glass. 



1. The abdominal appendages, excepting the hindmost, are 

 of small size, and serve in the female to carry the 

 eggs. The last or twentieth segment has no appen- 

 dages. 



XIX. The sixth abdominal appendages are broad and 

 lamellar, and form with the telson the powerful 

 tail-fin. 



i. The protopodite is short, broad and undivided, 

 ii. The endopodite is a flat oval plate, fringed at 



its free edge with setae, 

 iii. The exopodite is similar, but larger, and divided 



by a transverse hinge into two parts. 



XVIII. The fifth abdominal appendage is a small 

 swimmeret. 

 i. The protopodite is two-jointed, the small proxi- 

 mal joint being named eoxopodite, the longer 

 distal joint, the basipodite. 

 ii. The endopodite is a many-jointed filament 

 covered with setse. Its first joint is the 

 largest. 

 iii. The exopodite is similar, but smaller. 



XVII. and XVI. These two pairs of appendages closely 

 resemble XVIII. 



