144: THE BIOLOGY OF THE ANIMAL 



modified ? Note the ingrowth or endosternite, 

 internal to the bases of the appendage. Do you 

 find on the abdominal segments anything corre- 

 sponding to the endotergites and endosternites ? 

 Do you find any soft parts — e. g., muscles — at- 

 tached to the latter? Compare the epimeron 

 with that of the abdominal segment. What dif- 

 ference in size ? In direction ? ISTote that it 

 forms the inner wall of the branchial chamber, 

 and bears an ingrowth or endopleurite. What 

 is attached to the latter? If you regard the 

 outer wall of the branchial chamber Q)ranchioste- 

 gite) as composed of united pleura, do you like- 

 wise regard the inner wall as consisting of fused 

 epimera ? Why ? Counting only the sterna, how 

 many segments can you find in the cephalotho- 

 rax? Do you find a pair of appendages to cor- 

 respond to each sternum ? Are the sterna mova- 

 ble upon one another ? 



Draw the section of the thorax as seen from the end, 

 also from the under side. 



The last section of the abdomen is called 



III. The telson.— What is its shape? Color? What 

 differences between the tergal and sternal sur- 

 faces ? Does it bear any appendages ? Note the 

 structure of its margin. Compare it in shape, 

 size, and structure with the other sections of the 

 abdomen. Is the telson a segment? Note the 

 opening (anus) on its under side. Try to find a 

 hardened portion, the peri-anal plate, on each 

 side. 



G. The appendages. — By cutting through the articular 



