ZOOLOGY DIEECTIONS 



6. How many segments in the abdomen ? How many have 

 appendages? These appendages are called the sivimmerets. 



III. Homologies of the Appendages 



In this entire section where drawings are asked for they are 

 to be ventral views of the appendages from the left side of the 

 body. 



1. Study one appendage of the third abdominal segment. 

 Distinguish the stem or profopodite, composed of a basal short 

 segment, the coxopodite, and a long segment, the tasipodite. Of 

 the two branches given off from the end of the protopodite the 

 outer one is called the exopodite, while the one nearer the median 

 line of the body is called the endopodite. Draw X4 and label 

 all of the parts. 



2. Such a two-branched appendage is called a diramous ap- , 

 pendage, and constitutes the general plan upon which all of the 

 appendages of the crayfish are built. In the following study, 

 each appendage is to be studied in order to determine the modi- 

 fications which have arisen in the various parts of biramous 

 appendages. 



3. The study of homology usually involves a comparison 

 of organs or structures found in two different kinds of organ- 

 isms. When repeated parts upon the same individual show the 

 same fundamental plan of structure the term serial homology is 

 used. 



4. The terminal part of the abdomen is the ielson. The 

 telson, together with the appendage of the sixth abdominal seg- 

 ment, form the tail pi. Draw the entire tail fin X3, ventral view, 

 labelling all parts and being especially sure to show what parts 

 of the sixth abdominal appendage correspond to the parts worked 

 out for the third appendage under section 1. 



5. Remove carapace from the animal's left side exposing 



