LIFE HISTORY 



87 



are clearly defined, but tlio.se of the head-thorax are so 

 fused that they cannot be made out. The appendages of 



Figure 84. — Crayfish. 



the head-thorax region are the most important to the 

 animal. Certain of these are fin-like and by their constant 

 waving motion serve to carry food to the mouth. Others 

 are elongated and serve for walking. One pair, the 

 pinchers, are used for seizing 

 and holding. 



The last abdominal segment 

 and the appendages next to the 

 last are broad and fin-like and 

 together form a tail fin (caudal 

 fin) for use in thrusting the 

 animal backward, when it is 

 alarmed. 



78. Life History. — The sexes 

 are distinct. The males may be 

 distinguished from the females 

 by the larger tubular appendages 

 on the first and second segments 

 of the abdomen. The egr^s of the female are carried for 

 some time by the appendages of the abdomen, where they 

 pass through their early stages of development,. The 



Figure 85. — Molted Exo- 

 skeleton of lobster. 



