LOBSTER OK CRAYFISH 14 7 



find differences in the teeth on the inside of the jaws of 

 the forceps? Are these teeth fastened into sockets? 

 iN^ote the distribution of hairs along the margin and 

 over the surface. Is it different from the other append- 

 ages examined? Compare several specimens to see 

 whether or not the resemblances and differences are 

 constant. Draw. 



Can you give any reasons for considering as homol- 

 ogous the paired openings found on the thoracic ap- 

 pendages ? Review the five appendages on the other 

 side of the body and note their relative size, the various 

 directions in which they extend, the motions allowed 

 by their joints, etc. 



Remove the next appendage in front, the third max- 

 illipede or " foot-jaw." Can you find all the segments 

 represented in the great chela? In the last thoracic 

 appendage ? Does it have an exopodite ? A gill ? An 

 epipodite ? Note the bunch of bristles, the coxopoditic 

 setae. Are they on the coxopodite or epipodite? l!iote 

 the teeth on this appendage. How many segments 

 bear them ? What is their arrangement on each seg- 

 ment ? Study the distribution of the hairs. Draw. 

 Why is it called a " foot-jaw " ? 



Eemove the next two appendages, the second and 

 the first maxillipedes, and compare with the preced- 

 ing. Do you find any segments lacking? Which are 

 especially modified and how ? Draw each. 



Eeview all of the thoracic appendages and notice 

 again that they naturally fall into two groups. Give 

 what you consider to be the most characteristic struct- 

 ural features of each group. On what grounds do you 

 divide them ? 



0. The head appendages. — Eemove the most poste- 



