78 LABORATORY DIRECTIONS 



These folds are fringed with hairs so that they form a strainer 

 or filter which prevents the passage of large food particles into 

 the intestine. Make drawing of gastric mill as dissected. 



14. Manipulate the mandibles and learn where the large 

 muscles are attached. Distinguish the tendons. 



NERVOUS SYSTEM 



1. The central nervous system consists of a chain of paired 

 ganglia extending the length of the body close to the mid-ventral 

 line. The ganglia of a pair are so closely applied that they ap- 

 pear as a single ganglionic mass. Locate the nerve chain near 

 the base of the abdomen. Trace it forward along the floor of 

 the thorax to a point where it enters a small canal. With a pair 

 of forceps pick away the parts of the endophragmal skeleton 

 which form the canal surrounding the nerve chain. 



2. The brain or pre-esophageal mass is a rather large 

 white body just behind and above the bases of the antennules. 

 This supplies nerves to the eyes, antennae, and antennules. 



3. The para-esophageal connectives are a pair or nerve 

 cords which connect the brain, around the esophagus with the 

 hinder part of the nervous system. Behind the esophagus they 

 are connected by a transverse commissure. 



4. The post-esophageal mass lies behind the mouth. It 

 supplies the mandibles, maxillae, and first and second maxillipeds 

 with nerves. 



5. The thoracic nerve chain consists of six ganglionic 

 masses, which supply nerves to the third maxillipeds and the 

 five pairs of walking legs. The first one lies very close behind the 

 post-esophageal mass. 



6. Trace the abdominal nerve chain with its six ganglionic 

 masses. 



7. Make a drawing to show the nervous system and label 

 all parts. 



