ABDOMINAL APPENDAGES. 145 



by the end of the rectum, (2) the post-anal plate, 

 (3 and 4) the two furcal styles which project 

 backwards at the junction of (1) and (2). 



C. The Appendages. 



These are all reducible to a common type composed of the 

 three parts, protopodite, exopodite, and endopodite, already 

 seen in the appendage of the typical segment, together with 

 an epipodite, which may be a simple plate or may bear gill 

 plumes. From such a typical form all 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. 



Remove the appendages of the right side one by one, beginning 

 with the hindmost, and taking special care to remove each appen- 

 dage entire by cutting round the inner side of its attachment 

 to the body. The characters of the smaller ones can be best made 

 out by examination in a drop of water, between two slips 

 of glass. Place them in corresponding positions and draw 

 them. 



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 

 appendages. 



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. 



